The six senators seeking the White House can talk the talk. Voting the vote is not so easy.

Every four years, the allure of presidential politics tends to draw at least a senator or two away from legislative business, although none has won the White House since John Kennedy in 1960.

This time, the White House campaign has greater potential for consequences in the Senate, which is divided by the narrowest of margins, making every vote even more valuable.

So far, the senators who are absent to campaign for the White House haven't made a difference in whether a measure passed or not. The candidates say they are committed to be there if they are needed, and they've had to juggle their schedules to make some important votes.

The candidates _ four Democrats and two Republicans _have made varying efforts to be on hand for the 228 votes so far this year. The two Republicans, serving in the minority, have shown the most willingness to take off for the campaign trail.

Sen. John McCain of Arizona has missed about half the votes _ 117 as of Tuesday _ according to a count by The Associated Press. Sen. Sam Brownback of Kansas has missed about one-third, or 81. Only South Dakota Democratic Sen. Tim Johnson, recovering from a debilitating brain hemorrhage, has missed more.

Brownback spokesman Brian Hart said his boss was prepared to leave an Iowa bus tour last week to vote. It looked like he might be needed to help block an attempt to override President Bush's veto of legislation that would ease restraints on federally funded embryonic stem cell research.

But the vote was delayed for now. No matter what the issue, Hart said, "He would try his best to come back for any vote where he was absolutely needed for the outcome."

So far, Sen. Hillary Rodham Clinton, D-N.Y., has been the star pupil in the class of senators vying to be president when it comes to voting, missing just five votes since January. But she acknowledges that will change as the primary race heats up in the second half of 2007.

"I'm trying to, for as long as possible, maintain a commitment both to my Senate duties and, of course, to the campaign," Clinton said. "But there will be times when I will miss votes. There's no doubt about that."

Initially, Sen. Barack Obama had kept up with Clinton's attendance record _ through March each of them had only missed three votes. But the Illinois Democrat's absenteeism picked up in April (four missed votes), May (six missed votes) and June (10 so far), bringing him to 10 percent of votes missed so far this year.

Sens. Joe Biden, of Delaware, and Chris Dodd, of Connecticut, have missed more votes, but they have had to hustle harder in the Democratic primary as they campaign in the shadow of Obama and Clinton. They also have less money than the front-runners to pay for private planes and must fly commercial more often, cutting into their time in the Senate. The two have each missed about a quarter of the votes _ 62 for Biden and 59 for Dodd.

Besides the six senators, the list of White House hopefuls includes four House members: Democrat Dennis Kucinich of Ohio, and Republicans Duncan Hunter of California, Ron Paul of Texas and Tom Tancredo of Colorado.

With 435 members, the outcome of House votes hinge on a single member far less often than in the Senate. Democrats also have a slightly more comfortable majority in the House.

Besides votes, the candidate-lawmakers also struggle with committee assignments and constituent needs.

Senate Majority Leader Harry Reid of Nevada has said he expects their elected duties to come before presidential politics. The Democrats had a close call this spring when Reid scheduled a vote on a bill that would begin troop withdrawals from Iraq the same day as their first debate. There were fears they would have to miss the event, but the vote came early enough for each to be in the chamber, then fly on separate jets to South Carolina.

The four Democratic senators interrupted a Saturday of campaigning in February to cast a symbolic vote against Bush's effort to boost troop levels in Iraq. Brownback was also there on the side of Republicans who successfully blocked the resolution, but McCain decided to stay in Iowa rather than be there for what he called a "meaningless" vote.

The inevitable conflict between the demands of a presidential campaign and the responsibilities of public office is a recurring issue in elections. In 1996, Republican Bob Dole resolved the conflict by giving up his seat as Kansas senator when it became clear he would be the GOP presidential nominee.

In 2004, then Massachusetts Gov. Mitt Romney, now a Republican candidate in the 2008 race, pressured Democratic presidential candidate John Kerry to resign his Senate seat so the state would have a more reliable voter representing its needs. Kerry declined to do so.

The demands of campaigning have sometimes led to a gap between candidates' rhetoric and their actions. For example, four candidates _ Obama, Biden, Dodd and McCain _ have said Alberto Gonzales must give up the attorney general's post.

But when it came time for the Senate to express its displeasure formally with the nation's top lawyer last week, none of the four was around. Neither was Brownback, who has declined to seek Gonzales' resignation.

Clinton was the only presidential candidate to cast a vote on Gonzales, one of the seven times this year that she has been the lone 2008 hopeful to give a yea or nay.

Republicans were able to block Gonzales' opponents from raising a no-confidence vote, a symbolic effort without any ability for Congress to force the attorney general from office short of impeachment. Even if all the presidential candidates were around, they wouldn't have been able to come up with the seven votes needed to move the resolution forward.

Democratic consultant Dan Gerstein, who worked for Connecticut Sen. Joe Lieberman during his presidential campaign four years ago, said there is a risk to being absent because voters don't like to hear their senator is not showing up to do their work. But he said candidates can make up for the absences if they have strong political support in their states.

"The best thing a candidate can do is to be up front with his constituents that he will have to miss votes, make clear that they will be there for the big ones, and then work like heck to show the people at home that they and their staffs are still every bit as effective in delivering appropriations, cutting through bureaucratic red tape, and generally getting their job done," Gerstein said.

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Voting records available at http://www.senate.gov