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.
(CNN) -- In one of the unexpected moments from the past few weeks, some defenders of Wisconsin Gov. Scott Walker's attack on public unions have pointed to President Franklin Roosevelt.
Patrick McIlheran of the Journal Sentinel wrote, "Somewhere, Franklin Delano Roosevelt is grinning past his cigarette holder at Wisconsin's governor. They are on the same page regarding government unions."
These commentators have noted that Roosevelt's doubts about public sector unions suggest that today's conservatives are more in touch with his positions than the Democrats.
Yet during the past few months, the nation has actually been witnessing a rather fierce assault on the liberal tradition that FDR helped to create. It is hard to imagine that FDR would actually be grinning if he could see what is taking place.
At the most basic level, FDR argued that the government had a central role in American life. The government, he said, was needed to provide a floor of security to all Americans and to reduce some of the extreme risks that citizens faced in a market-based economy.
As FDR told the Democratic convention in 1936, "Better the occasional faults of a government that lives in a spirit of charity than the consistent omissions of a government frozen in the ice of its own indifference." FDR brought together a coalition that included organized labor, farmers, intellectuals and urban politicians to support his programs.
This liberal tradition is under assault. This is nothing new. Liberalism has been playing defense for several decades since the conservative movement took hold of American politics in the 1970s.
But following the 2008 election, when a progressive pragmatist became president along with a Democratic Congress, conservatives have intensified their attacks on a number of fronts.
The first has been at the state level. Walker has been at the forefront of a push by a number of Republican governors who are taking on public sector unions. These efforts are as much about curtailing the power of these unions as they are about reducing the state deficits.
But unions, as FDR and these governors realized, have been central to the political strength of contemporary liberalism. The unions have been the most reliable and consistent political force pushing for policies that boost the wages and protect the jobs of average Americans.
Historically, unions have also been one of the strongest supporters of other kinds of progressive policies as well, such as health care and education reform. Although union ranks have thinned in the private sector, public unions have grown.
Should the governors succeed in their effort, they would undercut a crucial part of the liberal coalition. During a conversation with a prank caller, who Walker believed to be the conservative billionaire David Koch, Walker revealed that this standoff was about much more than budgets.
He compared his actions to Ronald Reagan's decision to fire the air traffic controllers in 1981: "To me that moment was more important than just for labor relations or even the federal budget, that was the first crack in the Berlin Wall and the fall of Communism because from that point forward, the Soviets and the Communists knew that Ronald Reagan wasn't a pushover. And I said this may not have as broad of world implications, but in Wisconsin's history -- little did I know how big it would be nationally -- in Wisconsin's history, I said this is our moment, this is our time to change the course of history."
The second attack on liberalism has emanated from the courts with the recent challenges to President Obama's health care reform. While the "death of liberalism" since the 1960s has been greatly exaggerated, it is true that liberals did not experience much success at creating new government programs.
Liberals were much better at protecting existing programs, such as Social Security, than building new ones. That was what was so striking when President Obama succeeded at pushing through Congress a broad health care reform package which is one of the most extensive pieces of domestic legislation since the Great Society.
While many supporters initially dismissed the potential for a court threat, the legal challenge has proven to be more severe than anticipated. Republican presidents have been appointing more conservative justices for several decades now, and the strategy is paying off. Although several courts have upheld the law, several others have not and the case is likely to end up at the Supreme Court, where conservative justices are in the majority.
A federal judge in Florida struck down the health care law as unconstitutional and argued that the entire package needed to be redesigned. "I must reluctantly conclude that Congress exceeded the bounds of its authority in passing the Act with the individual mandate. Because the individual mandate is unconstitutional and not severable, the entire Act must be declared void," wrote U.S. District Judge Roger Vinson, who was nominated to the bench by President Reagan in 1983.
Finally, the Republicans have successfully shifted debate in Washington away from the politics of creating new programs and toward the politics of deficit reduction. The need to cut the deficit through spending reductions has become the central topic on Capitol Hill. While President Obama has argued over how much and where to make cuts, he has embraced the agenda of deficit reduction as an immediate, rather than long-term, priority.
The politics of deficit reduction usually don't work in favor of liberalism. A focus on the deficit creates a context both for cutting programs and for preventing Congress from updating and fully funding existing policies. During the 1980s and 1990s, for instance, the minimum wage remained on the books but greatly diminished in value when Congress failed to update the rates.
These are difficult days for liberalism and there is danger ahead. The question is much broader than whether President Obama will be re-elected or if Democrats can take control. Rather, what we are seeing is a rather strong assault by conservative forces against the political and policy foundations of the liberal coalition.
The opinions expressed in this commentary are solely those of Julian E. Zelizer.