Julian E. Zelizer is a professor of history and public affairs at Princeton University's Woodrow Wilson School. He is the co-editor of "Rightward Bound: Making America Conservative in the 1970s" and is completing a book on the history of national-security politics since World War II, to be published by Basic Books.
Julian Zelizer says presidents have 100 days to make an impact and are judged by that standard.
PRINCETON, New Jersey (CNN) -- When presidents enter the White House, they have approximately 100 days to show what they are made of.
The notion of a "hundred days" is an artificial creation of Franklin Roosevelt after he became president in 1932 in the Great Depression. But it has become a benchmark for evaluating the early success of a president.
The term is more than symbolic. Some presidents have been able to do a lot with those hundred days. Not surprisingly, Roosevelt was the most successful we have seen. His hundred days lasted from March 9 to June 16, 1933, and Congress passed 15 major bills.
Roosevelt, in a period of experimental genius, found support from Congress for a series of programs to help stabilize an economy where 25 percent of the work force was unemployed and banks were imploding as panicked citizens pulled out their money.
The humorist Will Rogers joked that "Congress doesn't pass legislation any more, they just wave at the bills as they go by," though in reality Democratic leaders were instrumental in initiating many of the ideas that came from the White House and making sure that they passed by sound margins.
Roosevelt understood that he had a limited window of opportunity after his election, and he moved fast. "I do not see how any living soul can last physically going the pace that he is going," said Hiram Johnson, "and mentally any one of us would be a psychopathic case if we undertook to do what he is doing."
Over the hundred days, Democrats remade the face of the federal government. Programs were created to regulate Wall Street and banking, support agriculture and labor, provide public works employment, regulate production and more.
Through the legislation, as well as his historic fireside chats, Roosevelt restored confidence in the government itself, as Americans sensed that Washington could save American capitalism. He also used the first months to overcome the many divisions that existed within the Democratic Party.
Lyndon Johnson had a very different kind of hundred days when he took over after the assassination of John F. Kennedy in November 1963. Johnson used his hundred days to define his presidency in relation to his predecessor.
Kennedy had encountered considerable trouble passing most of his legislative agenda, including civil rights and tax cuts, because a conservative coalition of Southern Democrats and Republicans blocked his proposals.
Johnson believed that in the months after the assassination, he needed to link himself to the deceased president, who seemed to become more popular after his death, and he used that connection to build political support for his bills. This is why Johnson retained the services of many Cabinet officials from the Kennedy administration.
"I needed that White House staff," Johnson recalled, "Without them I would have lost my link to John Kennedy, and without that I would have had absolutely no chance of gaining the support of the media or the Easterners or the intellectuals. And without that support I would have had absolutely no chance of governing the country."
During his first speech to Congress after the assassination, Johnson invoked the memory of the slain president by asking legislators to help him fulfill the unfinished agenda.
Calling Kennedy "the greatest leader of our time," Johnson said to Congress, "Let us continue." The memory of Kennedy helped him succeed in passing legislation on civil rights, tax cuts and the War on Poverty.
Yet another way to use 100 days is to undermine your partisan opposition in Congress. Ronald Reagan did this masterfully when pushing for his across-the-board tax cut in 1981, a centerpiece of his domestic agenda. Reagan argued that tax cuts would stimulate economic growth.
The president used the bully pulpit to overcome opposition among House Democrats, building support for the cuts. He gave a speech on television, urging citizens to write their legislators and tell them to support the cuts.
House Democrats, now the sole base for the party in Washington, joined in once they saw the public pressure. In fact, they pushed for tax cuts of their own, which were rolled into the bill.
"It's like the arms race between the United States and the Soviet Union," according to Michigan Democrat William Brodhead, "for every move there's a countermove; for every weapon, a counterweapon." By the end of the bidding process, Reagan could claim victory on Capitol Hill and his key legislation had drawn the support of his opposition.
Sometimes presidents have stumbled in the hundred days, and the results are disastrous. Jimmy Carter is one of the most striking examples. In his hundred days, Carter did almost everything wrong. One of his biggest failures was how he handled relations with Congress.
Trying to strengthen his credentials as a reformer, Carter took aim at pork barrel spending, opposing specific items that President Ford had included in his final budget that funded more than 300 water projects across the country. Carter dismissed the proposal as a classic example of congressional pork. He sent a letter to Congress stating that 19 of the projects would be cut.
Congress was furious. They believed these funds were essential to their constituents. Those affected by Carter's list included Sen. Russell Long, the powerful chairman of the Senate Finance Committee. The Senate overturned Carter's decision. Bitter feelings remained and the rocky relations continued to be a major problem for Carter.
The new president, whether Barack Obama or John McCain, can learn a lesson from all of these presidents about how to break out of the gridlock that has bogged down Washington. They will have to use their hundred days to build confidence in the government and its ability to stabilize the economic system, taking advantage of the narrow window they will have to get legislation through.
The new president will have to define himself in relation to his predecessor, but in this case by demonstrating clearly to the public what he will do differently, rather than the same, as President Bush. And, finally, the new president will need to find legislation that attracts some support from the opposition to diminish the power of polarization on Capitol Hill and establish the groundwork for future compromise.
The one thing that Obama or McCain must realize is that those hundred days will disappear quickly. Once they are gone, as Bill Clinton learned after delaying his push for health care reform, the political capital is hard to get back.
The opinions expressed in this commentary are solely those of Julian Zelizer.