Charlotte, North Carolina (CNN) -- President Barack Obama accepted his party's nomination for re-election on Thursday, telling the Democratic National Convention and Americans that only the voters in November have the power to secure the change he started.
In a tough speech that sounded now-familiar themes of his campaign, the president sought to show his supporters that their votes for him four years ago brought achievements that would be wiped out if Republican challenger Mitt Romney wins the election two months away.
"If you turn away now -- if you buy into the cynicism that the change we fought for isn't possible, well, change will not happen," Obama said, depicting a scenario in which special interests and conservative politicians run Washington and the country. "... Only you can make sure that doesn't happen. Only you have the power to move us forward."
Acknowledging the nation's hope has been tested since he first addressed the party conclave in 2004 as the keynote speaker, Obama urged Americans to look beyond the "trivial" nature of election campaigns to fully grasp the magnitude of the election.
"When all is said and done -- when you pick up that ballot to vote -- you will face the clearest choice of any time in a generation," he said. "Over the next few years, big decisions will be made in Washington, on jobs and the economy; taxes and deficits; energy and education; war and peace -- decisions that will have a huge impact on our lives and our children's lives for decades to come."
It is more than a choice between two candidates or parties, he said, calling it "a choice between two different paths for America, a choice between two fundamentally different visions for the future."
The Romney campaign responded by saying Obama continued to offer polices that haven't worked under his presidency, which has seen high unemployment, a sluggish economic recovery and rising federal deficits and debt.
"Americans will hold President Obama accountable for his record -- they know they're not better off and that it's time to change direction," the Romney campaign statement said.
CNN Chief Political Analyst Gloria Borger called Obama's speech "defiant at every single level," particularly its criticism of Romney's lack of experience on foreign policy, while CNN Senior Political Analyst David Gergen said Obama was "presidential" but offered little new in the way of specific promises.
Republican strategist Ari Fleischer, also a CNN contributor, said the speech contained the same themes and promises of the past four years."
Obama called for the nation to rally around "a real, achievable plan" to deal with the economic challenges that are the most problematic issues facing his campaign.
Specific goals included creating 1 million new manufacturing jobs by the end of 2016, halving net oil imports by 2020, cutting the growth of college tuition in half over the next 10 years, training 2 million workers for jobs and supporting natural gas development that can employ 600,000 people by the end of the decade.
Three of the goals are new -- the increase in manufacturing jobs, the cut in college tuition increases and the reduction in oil imports -- while the others have been previously discussed by the president or his administration.
"I won't pretend the path I'm offering is quick or easy. I never have," Obama said, adding "it will take more than a few years for us to solve challenges that have built up over decades."
In an obvious message to independents and moderate voters of both parties, Obama sought to distance himself from the accusation by Romney that he is a big-government liberal.
"Those of us who carry on his party's legacy should remember that not every problem can be remedied with another government program or dictate from Washington," Obama said.
Following the theme of the forceful endorsement he received Wednesday night from former President Bill Clinton, Obama also offered an optimistic outlook for the future to contrast with Republican warnings of a nation in peril.
"We don't think that government can solve all our problems," he said. "But we don't think that government is the source of all our problems -- any more than are welfare recipients, or corporations, or unions, or immigrants, or gays, or any other group we're told to blame for our troubles."
He claimed founding principles as the dominion of Democrats as well as Republicans, declaring that "we, the people, recognize that we have responsibilities as well as rights; that our destinies are bound together; that a freedom which only asks what's in it for me, a freedom without a commitment to others, a freedom without love or charity or duty or patriotism, is unworthy of our founding ideals, and those who died in their defense."
Obama also delivered some biting criticism of Romney and his running mate, conservative Rep. Paul Ryan of Wisconsin, saying their economic plan of tax cuts and shrinking government will undermine the economy rather than promote growth.
He mocked the GOP mantra on tax cuts that he said had helped bring the recession he faced when he took office, describing the Republican remedy for growth as "take two tax cuts, roll back some regulations, and call us in the morning."
Obama also made fun of Romney for calling Russia the nation's biggest foreign threat and other recent gaffes on the former Massachusetts governor's trip to England, Israel and Poland.
"In a world of new threats and new challenges, you can choose leadership that has been tested and proven," the president said, citing the killing of Osama bin Laden and ending of the war in Iraq as accomplishments.
Earlier on the final night of the three-day Democratic convention, other speakers delivered fiery criticism of Romney and Ryan while praising Obama for his leadership in the face of multiple crises upon taking office.
Veteran Sen. John Kerry of Massachusetts, the unsuccessful Democratic presidential nominee in 2004, drew howls of delight when he answered Republican claims that the nation is worse off under Obama by noting the president's most visible foreign policy achievement.
"Mitt Romney said it would be 'naïve' to go into Pakistan to pursue the terrorists," Kerry said. "It took President Obama, against the advice of many, to give that order and finally rid this earth of Osama bin Laden."
To rising cheers, Kerry declared: "Ask Osama Bin Laden if he is better off now than he was four years ago."
Former Michigan Gov. Jennifer Granholm criticized Romney for opposing a government bailout of the nation's auto industry amid the financial crisis of 2008-2009, saying Obama showed the leadership to save vital jobs for the country by taking a politically unpopular step.
Romney "saw the same crisis and you know what he said -- let Detroit go bankrupt," Granholm said. Referring to Romney's Michigan roots and his personal wealth that includes a car elevator at one of his houses, she said he "loves our lakes and our trees, he loves our cars so much they even have their own elevator, but the people who design and build and sell those cars ... well, in Romney's world, the cars get the elevator and the workers get the shaft."
The night also included some celebrity influence, as Marc Anthony sang the national anthem after James Taylor entertained the delegates with old hits "Carolina In My Mind" and "You've Got A Friend," the later performed after he described himself as an "old white guy" who loves Obama.
In an emotional moment, former Rep. Gabrielle Giffords of Arizona, who was grievously wounded in a shooting at a campaign event in January 2011, led the Pledge of Allegiance.
Clearly debilitated by her head injury, Giffords walked with Rep. Debbie Wasserman Schultz to the front of the stage and loudly recited the pledge, using her left hand to hold her right hand to her heart. The delegates stood, some openly in tears, and joined her.
Vice President Joe Biden had tears in his eyes when his son, Beau, the Delaware attorney general, nominated him for the party ticket and the packed arena shouted its acclamation. Biden later delivered his own powerful speech that attacked Republicans for denigrating government loans and job training programs.
"They seem to think you create a culture of dependency when you provide a bright, young qualified kid from a working family a loan to get to college, or when you provide job training in a new industry, for a dad who lost his job, because it was outsourced," Biden said.
Obama's speech concluding the convention originally was set for the 73,000-seat Bank of America Stadium, but possible thunderstorms caused organizers to move it indoors to the smaller Time Warner Cable Arena, where the political conclave has taken place so far.
In a conference call on Thursday with supporters who had credentials for the outdoor venue but won't be able to get into the arena, Obama acknowledged their disappointment, which he said was shared by "crestfallen" campaign staff who worked for months organizing the scuttled stadium event.
"You're doing unbelievable work in this close race," the president told grassroots campaigners registering voters in North Carolina and across the country. "We can't let a little thunder and lightning get us down. We have to roll with it."
On Wednesday night, Clinton thrilled an overflow convention crowd by picking apart Republican attacks on Obama and explaining why the president, if re-elected, can achieve the same economic growth that Clinton did in the 1990s.
Clinton said the man who defeated his wife, Hillary, for the Democratic nomination four years ago offers a better path forward for the country, and framed the November election as an opportunity for voters to choose what kind of country they want.
"If you want a winner-take-all, you're-on-your-own society, you should support the Republican ticket," Clinton said. "If you want a country of shared prosperity and shared responsibility -- a we're-all-in-this-together society -- you should vote for Barack Obama and Joe Biden."
The speech was vintage Clinton, blending an expert's command of figures and details with a down-home touch of language and emotion that made him one of the best communicators and politicians of his era.
In response, the Romney campaign said that speech drew a "stark contrast" between the two-term Democratic president's accomplishments and those of Obama in what it called "the worst economic record of any president in modern history."
Clinton takes aim at Republicans
Ryan told a campaign event Thursday in Colorado that he and Romney want the election to be about a better path, rather than "the lesser of two evils."
"We want you to have an affirming choice," Ryan said, describing the options as the Republican plan for an "opportunity society with a safety net and a path to prosperity" or a Democratic alternative for a "welfare state with a debt crisis."
Ryan's comments contained traditional conservative themes and policies that defined the Romney campaign through last week's GOP convention that nominated the former Massachusetts governor and Ryan, the House Budget Committee chairman from Wisconsin.
Self-inflicted wounds for Democrats
The convention included triumphant speeches by Clinton and first lady Michelle Obama, but also some self-inflicted wounds for Democrats. First, campaign organizers announced they were moving Obama's address to the indoor venue, preventing tens of thousands of credentialed supporters from attending.
Later, the Wednesday convention session started with some dissension when delegates approved a change in the party platform to reinstate language recognizing Jerusalem as the capital of Israel. The original platform approved Tuesday omitted that reference, which had been part of the 2008 platform, and Republicans quickly criticized it as a snub to Israel.
Another change restored the word "God" to the platform after the 2012 version omitted it, though it included language on faith as part of American society. The language referring to God-given rights was the same as in the 2008 platform.
It took three voice votes, with supporters and opponents of the changes strongly expressing their preference, before a clearly flummoxed Los Angeles Mayor Antonio Villaraigosa declared himself satisfied that a two-thirds majority backed the new language, despite groans of displeasure from some delegates.
A senior Democratic source told CNN that Obama intervened to change the platform language, saying the president "didn't want there to be any confusion about his unshakeable commitment to the security of ... Israel." In addition, Democratic sources said Obama also asked aloud why the word "God" had been dropped.
"The platform is being amended to maintain consistency with the personal views expressed by the president and in the Democratic Party platform in 2008," said a statement by Wasserman Schultz, who heads the Democratic National Committee.
Struggle to define election
Both campaigns are fighting to define the election in the minds of voters. Republicans want it to be about Obama's presidency, while Democrats seek a choice between differing political ideologies on the size and role of government.
In particular, Republicans seek to shrink the size of government and end chronic federal deficits and rising national debt through reducing spending, reforming entitlement programs such as Social Security, Medicare and Medicaid, and slashing taxes on businesses and many individuals as a spur for economic growth.
Obama and Democrats argue that a deficit reduction plan also needs additional revenue, and they propose allowing tax rates on income of more than $250,000 for families and $200,000 for individuals to return to the higher levels of the 1990s.
Republicans oppose any kind of tax increase, and the impasse over that issue has been the main impediment to a comprehensive deficit reduction agreement during Obama's first term.
The race overall is very tight, with a new poll Tuesday showing Romney received little bounce from last week's convention intended to introduce him to voters just now turning their attention to the presidential race.
The CNN/ORC International Poll also indicates that less than 40% of registered voters said the GOP convention made them more likely to vote for Romney. At the same time, Romney got a slight bump in his favorable rating, and on being in touch with the middle class and women, although he still trails Obama on those two questions.
CNN's Kevin Bohn, Jessica Yellin, Dana Bash, Ashley Killough, Kevin Liptak, Sarah Aarthun, Halimah Abdullah, Paul Steinhauser, Adam Aigner-Treworgy, Brianna Keilar and Peter Hamby contributed to this report.