Editor's note: Julian E. Zelizer is a professor of history and public affairs at Princeton University. He is the author of "Jimmy Carter" (Times Books) and editor of a book assessing former President George W. Bush's administration, published by Princeton University Press.
(CNN) -- When Sen. Ted Kennedy died in August 2009, many Democrats wondered who would replace him as the voice of modern liberalism. With a Democratic president who was then fighting for an ambitious health care program, many felt Barack Obama would be that voice.
But over the past few months Obama has not filled this role, as became clear during the debate over the debt ceiling. Other than a handful of party officials, led by House Minority Leader Nancy Pelosi, the silence of liberalism has been striking.
Since Republicans won control of the House of Representatives in 2010, Democrats have been acting like a football team that starts the game so focused on not allowing the other team to score that they themselves don't have much of a plan for how to score.
One factor that allowed the GOP to rebound from the devastating loss it faced in 2008 was its ability to come together around a handful of ideas that animated supporters.
During the debate over the debt ceiling and deficit reduction, Republicans hammered home their point. The message was simple: Government is bad and the deficit had become a huge threat to the stability of the nation. If the deficit was not reduced quickly, the country would suffer. Layered onto this argument was the claim that tax increases needed to be off the table, or they too would ruin any chance of economic recovery.
The essence of the Democratic response, certainly from the White House, was that they disagreed on the size of the cuts that were needed. Obama also put up a half-hearted case for raising revenue on the wealthy, though he has done little over the last year to try to get that passed.
Indeed, in December, the last time Democrats controlled both houses of Congress, Obama agreed to extend President George W. Bush's tax cuts for the wealthy.
The irony is that liberals often have public opinion on their side. Yet Democrats are frequently scared to say what a majority of Americans think.
Polls show consistently that the public has favored raising taxes on the wealthy to help lower the deficit. Polls also show that voters like and expect many of the government services that Republicans have moved to cut. Jobs, not deficits, are the No. 1 concern. Polls have shown that the public was unhappy with the performance of the GOP during the debt ceiling crisis and they have negative views of the Tea Party.
What are some the arguments that most of the top Democrats failed to make as the debt-ceiling crisis unfolded?
The first was to challenge the basic assumption that this is the right time to cut government spending. Many economists have warned that pulling money out of the economy and cutting government jobs are the wrong things to do during a struggling recovery. Obama risks repeating the mistake of President Franklin D. Roosevelt, who tried to balance the budget in 1937, only to throw the economy into a recession.
As Wall Street reacted to poor manufacturing reports the day of the debt deal, there was evidence that deficit reduction is not the magic bullet Republicans had promised and that revitalizing the economy -- along with the higher tax revenue it would generate -- is really the best way to restore confidence.
The second argument that Americans rarely hear from Democrats is that government is good. For all the talk coming from Republicans about how the fiscal crisis in Greece proves that government must be sharply cut back, Democrats could provide an equally compelling case about how a social safety net and investment in infrastructure has played a vital role in promoting healthy economies. They could point to America's incredible growth in the 1940s and 1950s, which would have been impossible without government investment.
The final argument is about the need for tax increases. Republicans claim that any tax increase would stifle growth. Many respected economists, from all sides of the political spectrum, disagree. Among experts, there is a realization that real deficit reduction will require revenue increases, not just spending cuts.
In previous eras, Democrats were willing to put forward arguments to defend taxes. Roosevelt argued during World War II that Americans had to sacrifice for the general good of the nation. In 1967 and 1968, Lyndon B. Johnson claimed that a wealthy nation could afford to contribute more to the common good for the pursuit of domestic policy and foreign policy.
Unless Democrats start to put forward some ideas of their own, they will suffer at the ballot box. In the end, most Americans want something to vote for, and candidates they can believe in.
Candidate Obama realized this in 2008 and used it to defeat Sen. Hillary Clinton in the primaries. As president, Obama has acted very differently and risks intensifying the ideological vacuum that has caused so many problems for his party.
The opinions expressed in this commentary are solely those of Julian E. Zelizer.