Editor's note: Julian E. Zelizer is a professor of history and public affairs at Princeton University. He is the author of "Jimmy Carter," published by Times Books, and editor of a book assessing former President George W. Bush's administration, published by Princeton University Press.
Princeton, New Jersey (CNN) -- In Wednesday's speech, President Obama, in what now has become his classic style, tried to thread the needle.
On the one hand, the president joined in the debate over reducing the deficit and debt.
On the other hand, he reminded voters of the importance of government spending. "We believe, in the words of our first Republican president, Abraham Lincoln," he said, "that through government, we should do together what we cannot do as well for ourselves." Even with these words, however, his focus was on cutting the deficit.
Obama offered his version of reform, one that would include cuts in defense spending, loophole-closing tax reform, a probable tax increase on the wealthy, and reforms to Medicare and Medicaid that avoid transforming the fundamental character of the program.
In the speech he defended government programs that support the elderly, the economically disadvantaged and government investment in the economy. He reminded his audience how voters like government services, although they don't often want to pay for them. He said Rep. Paul Ryan's, R-Wisconsin, plan would extend tax cuts for the wealthy while raising the costs seniors must pay for health care. He said, "That's not right and that's not going to happen as long as I'm president."
But Obama has made ringing speeches before against extending the Bush tax cuts and then given ground in negotiations with Republicans. After all, that's why the tax cuts were extended. He will need to draw some lines in the sand after this speech so it doesn't happen again.
In his effort to respond to the Republican challenge on spending, President Obama must be careful not to end up embracing their ideas in the quest for moderate voters during the negotiations.
Despite Obama's defense of government, it is very easy to see how the debate could change quickly. Facing election year pressure, the president could drop some of the proposals that cause too much political controversy, such as his promise not to extend President Bush's tax cuts for the wealthy. We have seen Obama do this before with the extension of the tax cuts during the lame duck session of Congress (as well as on other issues like Guantanamo).
If Obama gives away too many of the proposals that make his a "Democratic" version of deficit reduction, and signs on to too much of Ryan's plan during the negotiations, he would leave Democrats demoralized going into 2012. He would also hand Republicans a massive victory.
Simply on policy grounds, the kind of cuts Ryan envisions would have a massively detrimental impact on core programs that Democrats have supported for decades. According to Brookings economist Henry Aaron, Ryan's plan would double the amount of health care costs paid by enrollees and halve Medicaid grants to the states by 2022.
The 32 million people who are scheduled to finally receive health care coverage as a result of Obama's reform would find themselves without any assistance. All the while, Ryan would cut taxes and leave the nation facing continued deficits in coming years. This would mean that a politically weakened president -- who would lack the enthusiastic support of his base -- would have to confront more spending cuts down the road.
With this speech, President Obama steps right into the political environment Republicans were hoping for. Washington is very far from the atmosphere that existed in 2009 and 2010, when growing government was still a politically viable option for Democrats. That period is over. Given that Obama has moved into Republican territory, he needs to draw some lines in the sand or he will simply become the type of Democrat too willing to compromise on basic principles that he promised not to be during the 2008 primaries.
The opinions expressed in this commentary are solely those of Julian Zelizer.