Editor's Note: Julian E. Zelizer is a professor of history and public affairs at Princeton University's Woodrow Wilson School. He is the author of "On Capitol Hill: The Struggle to Reform Congress and its Consequences, 1948-2000" and the editor of "The American Congress: The Building of Democracy." He is finishing a book on the history of national-security politics since World War II. He regularly writes for Politico, The Huffington Post and the Washington Independent.
Historian Julian Zelizer says it's good that the presidential candidates had to vote in real time on the bailout.
PRINCETON, New Jersey (CNN) -- Wednesday night's vote on the financial bailout was good for future legislators who plan to run for president. For decades, the conventional wisdom has been that sitting senators make bad presidential candidates.
Almost everything about the legislative process is rough and ugly, the thinking goes. Legislators compromise, take contradictory stands, strike deals with their adversaries and form unholy alliances. When the life of a sitting senator is exposed on the campaign trail, it doesn't usually look very good.
The last sitting senator to win an election was John F. Kennedy in 1960, and before him it was Warren Harding in 1920. James Garfield was a member of the House when he was elected in 1880. These were the only sitting legislators who have been elected.
In short, we have simply not had many success stories of sitting legislators running for office. Legislators can win, like Lyndon Johnson or Richard Nixon, but they usually need some time outside Capitol Hill before voters will elect them.
Although the Senate has been called the "presidential pre-school," it has been better for candidates to have graduated from first or second grade before they actually run for the White House. That way, candidates can point to another report card when boasting to voters and have some distance from their legislative past.
Governors have done much better in recent decades. This year will be different. Barring any dramatic event, we will have a sitting senator win the presidential election. This year, we are learning some of the virtues of having legislators in the contest. The convergence of the financial crisis last week and Wednesday night's Senate vote -- with both Obama and McCain present -- demonstrates why this kind of candidacy can be beneficial.
Simply put, legislators have to vote for things. Unlike a governor or a former legislator, sitting members have to make decisions as events unfold.
Because of their job, on critical issues they are forced to take a stand -- particularly as a real crisis unfolds in an election season -- on national issues, and this gives voters a better way to evaluate them. Sitting governors sometimes have to deal with these issues as well, but primarily at the state and local level.
From John McCain, we have learned a lot because of his vote and the events leading up to it. In terms of public policy, McCain has proved himself to be a conservative, like George W. Bush and many others, who is willing to use the federal government to achieve certain objectives.
After Wednesday night's vote, it will be difficult for him to make staunch anti-government arguments and expect that audiences will forget his vote for government intervention. In terms of his political style, we have learned that McCain can be brash and rash, use surprise and unpredictability as political tools, and put himself front and center when trying to work out a deal.
From Barack Obama, we have learned a lot as well. In terms of policy, we have seen that Obama is a liberal who is quite comfortable extending the reach of the federal government. He is also willing to shore up Wall Street and market forces, believing like many Democratic Leadership Council Democrats that the fate of Main Street and Wall Street are connected.
During the past week, Americans have seen that his political style is not at all similar to McCain's. Obama likes to work behind the scenes, favors a slower and more deliberate pace of negotiation, and is not as comfortable trying to force members of his party into a vote.
There have been other moments when sitting senators were forced to make decisions in the middle of a campaign that gave us clues to what kind of presidents they would be.
In October 1960, Coretta Scott King called John Kennedy's adviser Harris Wofford and asked for the Democratic candidate's assistance in gaining the release of her husband, Martin Luther King Jr., who had been sent to prison in Georgia after a protest for racial integration.
Wofford contacted Kennedy's brother-in-law Sargent Shriver, who urged Kennedy to aid King. Kennedy called Coretta King, conveying his sympathy.
The candidate's brother Bobby Kennedy was frustrated upon hearing the news, fearing that this would cost Kennedy key southern states, though he too thought that the arrest was unjust and bad for the nation. Bobby Kennedy called the judge, who allowed King to be released.
Historians believe that John Kennedy's call to Coretta King helped Kennedy with the African American vote in swing states like South Carolina. It demonstrated his willingness to help the civil rights cause, although it also suggested that his main tactic would be to work behind the scenes. Martin Luther King Sr., who learned about the call from Coretta, said the call was sufficient to cause him to leave the Republican Party.
In August 1964, Republican Sen. Barry Goldwater agreed to support the Gulf of Tonkin Resolution, which authorized the use of force in Vietnam. Through the summer, Goldwater had been attacking President Lyndon Johnson, a Democrat, for being weak on defense and for his policies in Vietnam.
Goldwater claimed that Johnson was secretly planning a war in Vietnam and, at the same time, was not prepared to use the military force necessary to actually win the battle. But after a private meeting with Johnson, Goldwater concurred that the Gulf of Tonkin Resolution was in the best interests of the country.
By doing so, he took a major issue -- Goldwater's criticism of how the administration was handling Vietnam -- off the table and undercut a centerpiece of his campaign against LBJ. The difference between the parties on Vietnam was not so great, as turned out to be the case in the coming years, when a bipartisan alliance moved us further and further into Vietnam.
Though the importance of this action might have been lost on most voters, Goldwater showed that he was willing to reach across the aisle despite his own pronouncements about extremism.
The 2008 election will bring victory for a sitting senator. Hopefully, with Wednesday night's vote, the nation learned a bit more about the virtues of having sitting senators in a presidential race as candidates were forced to make decisions on major issues in real time.
Neither Obama nor McCain has the luxury, as a governor would, of merely making promises about the future while sitting on the sidelines as a Monday morning quarterback about national issues in the present.
The opinions expressed in this commentary are solely those of the writer.