Editor's note: Julian Zelizer is a professor of history and public affairs at Princeton University. He is the author of "Jimmy Carter" and of the new book "Governing America."
(CNN) -- The stakes are high for Republicans at this week's convention. As the delegates gather in Tampa,the GOP needs to be ready to lay out a set of compelling arguments to frame the final months of the campaign.
More Americans will be paying attention to the campaign with the start of the conventions. With a new CNN poll showing that the Republican Party's favorability rating is down to 43 percent, the convention needs to strengthen the party's brand name. And since the convention will be a day shorter because of Tropical Storm Isaac, the GOP needs to make sure that it uses its time well.
If Republicans don't get the arguments right, they could easily miss the post-convention bounce they are counting on to give Mitt Romney some momentum after a rough summer.
Republicans need to make a compelling case that President Barack Obama's policies have failed to revitalize the economy.
Although it is clear that economic conditions are still not good, with slow growth and high rates of unemployment, there are alternative ways in which Democrats will depict this story. They will argue that President George W. Bush's economic policies, as well as the reckless practices of Wall Street, are to blame. In fact, Obama can argue he has done well in preventing catastrophe and that signs of economic improvement are evident.
Democrats might also blame Republican obstruction in Congress as another reason that economic recovery had stalled. Had Republicans not used the debt ceiling to force concessions on spending cuts, Democrats will say, more Americans could be working again.
Republicans, in contrast, will need to do to Obama what Ronald Reagan did to President Jimmy Carter in 1980. They will have to convince American voters that the president's policies are in fact to blame.
Reagan brilliantly pointed to Carter's regulatory and fiscal programs in explaining why the nation suffered from economic malaise. While most experts would agree that the problems of the era, such as the energy crisis, were not Carter's fault, Reagan and the GOP made this case well in their campaign.
As Reagan famously quipped, "Recession is when your neighbor loses his job. Depression is when you lose yours. And recover is when Jimmy Carter loses his."
It will also be essential for the speakers to offer an alternative path, especially if they don't want to get sidetracked with issues like the Todd Akin controversy.
What Republicans are pushing is economic conservatism -- namely, that tax cuts, deregulation, and spending cuts can improve economic conditions for most in this country. Reagan made this case in 1980 when he pushed for supply side economics as the cure-all solution to malaise. This is much harder to do today, especially because of the financial collapse that came toward the end of Bush's presidency, which for many Americans discredited conservative economic ideas.
With Mitt Romney surrounding himself with many of Bush's economic advisers, he and Paul Ryan will have to more than simply issue vague promises of how cutting and cutting government equates to a bountiful economy given President Bush's record.
Indeed, Democrats will warn that taking so much money out of the economy at this time through government spending cuts will have recessionary effects. If the GOP wants to counteract the image of a party intent on helping the top 1 percent, they need to make these connections for voters.
Unless Republicans want to be painted as extremists, they must rebut the ongoing charge that the party has moved far to the right. The addition of Paul Ryan to the ticket only added fuel to the fire of Democrats who have made this accusation.
The danger for Republicans is great. In 1964, Lyndon Johnson won in a landslide over Sen. Barry Goldwater by connecting him to the far right. Extremism, Johnson revealed, was certainly a political vice.
President Bill Clinton tapped into this playbook in 1996 during his run for reelection when he argued that Sen. Robert Dole, Speaker of the House Newt Gingrich, and the House Republicans were one and the same -- each seeking radical slashes in government that he said would harm middle- and working-class Americans.
One ad flashed the words "Dole," then "Gingrich," then combined them into one before listing all the different policies they wanted to eliminate. "Dole-Gingrich," the ad read, "Against Family Leave. Against a Woman's Right to Chose . . . Cutting vaccines for children. Against the Brady Bill and Assault Weapons ban. Against higher minimum wage. Cutting college scholarships."
Thus far Mitt Romney has had trouble pushing back against these charges. Even though his campaign started with the promise of a Republican who had the best chance to reach the vital center, rather than rival candidates like Newt Gingrich who seemed off center, the dynamics of the campaign have pushed Romney toward pleasing the base and his vice presidential nominee is associated with the tea party wing of the GOP.
Romney can't win if voters in states like Ohio, Florida and Wisconsin see him as off center. In his speech this week he will need to replicate the success of Reagan in his acceptance speech 1980 who, in just a few words, convinced Americans how a politician once seen as to the extreme right was in fact the person who could best unite a divided country.
"This convention," Reagan boasted, "has shown to all America a party united, with positive programs for solving the nation's problems; a party ready to build a new consensus with all those across the land who share a community of values embodied in these words: family, work, neighborhood, peace and freedom."
These are the challenges that Republicans face in the coming days and these are the arguments that the GOP must successfully make. If they can do this, they are likely to enjoy a healthy bounce and re-energize a campaign that has languished this summer.
If they don't, they are unlikely to make progress against a president whose tough and aggressive campaign has continually forced Republicans into a defensive position, even with an economy that is still struggling.
Follow @CNNOpinion on Twitter.
Join us at Facebook/CNNOpinion.
The opinions expressed in this commentary are solely those of Julian Zelizer