Senators who look in the mirror think they see the next president of the United States. History, however, has shown that the reflection is that of a losing candidate.

Running for president as a sitting senator is a great disadvantage, as the many senators who are about to throw their hat in the ring will find out. Hillary Rodham Clinton (D-N.Y.) and John McCain (R-Ariz.), however, are exceptions to this rule; their senate careers have positioned them well for 2008.

Only two sitting senators have ever won the presidency — John F. Kennedy and Warren Harding — and both had short and relatively undistinguished Senate careers. By contrast, consider the success of governors. Not only have four of our last five presidents been governors but incredibly none had even held a real job in Washington before entering the presidency.

The reasons for the success of governors and failure of senators are many. Governors are executives; they can speak and govern in their state as a president would. They are in charge, not one of a hundred. They do not have to cast votes on thousands of matters or lend their names to as many messy compromises, as senators do. Governors can also run against Washington, where senators are “part of the problem.”

Clinton and McCain are in a different boat, however, than George Allen (R-Va.), Evan Bayh (D-Ind.), Joe Biden (D-Del.), Sam Brownback (R-Kan.), Russ Feingold (D-Wis.), Bill Frist (R-Tenn.), Chuck Hagel (R-Neb.) and other senators who might run.

After leaving the White House, Clinton’s chances to be president were near zero. She was a polarizing figure who had never served in elected office on her own and whose views were to the left of her husband’s successful “new Democrat” political strategy.

The Senate has given Clinton tremendous stature. She has her own political office.

She has used her time in the Senate to wipe away the criticism that she would be popular with the Democratic base but could never win a general election. Representing New York during Sept. 11 allowed Clinton to show that she was tough and reminded people that she had been in the White House and understood the necessities of power. Her frequent dealings with Republicans have taken some of the edge off the perception of her as a strong partisan. But because she was so well-known and well-defined with the base of her party, she has been able to move toward the center and still remain credible to Democrats.

McCain electrified the campaign trail in 2000, but his loss in the primaries seemed to signal the end of his presidential chances. While appealing to moderates of both parties, McCain had real problems with conservatives in his own party, who distrusted his maverick tendencies.

But if you want to think of how McCain’s Senate career will help him, remember these three words: “reformer, pork buster, hero.” In a time of scandals, McCain and his reformer image is the perfect antidote to Jack Abramoff and other unsavory characters. McCain is not consorting with shady lobbyists; he is investigating them and bringing them down. Forgotten in the era of budget surpluses, McCain’s longtime opposition to earmarks and special projects will endear him to conservative voters in his party. Finally, McCain’s hero status gives him credibility on Iraq that far surpasses other Republican candidates. He can be tough, but different from Bush: “for winning in Iraq, but against torture.”

The Senate is not the traditional path to the White House, but Clinton and McCain may buck this trend. We could even see a first in American history, two sitting senators pitted against each other. It certainly wouldn’t be boring.

Fortier is a research fellow at the American Enterprise Institute.