By David Nather, CQ Staff

It’s only March, and you’ve just wrapped up the Republican presidential nomination. You still have a day job in the Senate, but you haven’t been there in ages. Do you:

A) Hang out in the Senate more?

B) Stay away from the place?

C) Drop by and cast your vote only when the leadership really, really needs you?

John McCain has made his decision and — officially — it’s Option C. His aides say he will try to put in an appearance at the Capitol whenever his participation in a roll call could determine the result. The Arizona senator “has a policy of always being present when his vote will affect the outcome, and that’s not going to change because he’s running for president,” said a campaign spokeswoman, Crystal Benton.

The way that’s likely to work out in practice, though, is really closer to Option B. By offering to show up for close votes, McCain might seem to be inviting all kinds of Democratic mischief, like luring him off the campaigning and fundraising trail to vote on potentially uncomfortable issues for him, such as the Iraq War or expanding children’s medical insurance coverage. In reality, though, there are few cases in which McCain’s vote would probably decide the outcome — and so his stated policy could be a clever way of accomplishing what most of his GOP colleagues advise: Stay far away.

“ John McCain ’s biggest advantage is that he’s viewed as an anti-senator,” says the chairman of the Senate GOP Conference, Lamar Alexander of Tennessee. “My personal advice would be for him to make his case outside the Senate.”

The same dilemma is bound to come up for either Barack Obama of Illinois or Hillary Rodham Clinton of New York — if their race for the Democratic nomination ever ends. For the first time in American history, both major-party candidates for president in 2008 will be senators, a fact that can only make partisans on both sides salivate at the opportunities to trap the nominees with embarrassing votes.

In most cases, though, Republicans probably won’t need McCain’s vote, which should make it easier for them to defend him against Democratic maneuvers. For one thing, the Senate gives the minority party so much power that GOP leaders have plenty of ways to block any legislation that starts moving in order to complicate life for McCain, says Don Stewart, a spokesman for Minority Leader Mitch McConnell of Kentucky.

Another factor is that, in a Senate where Democrats effectively control just 51 of the 100 seats — and any remotely controversial legislation needs 60 votes to overcome a filibuster — Majority Leader Harry Reid of Nevada is more likely than McConnell to need McCain’s vote. Majority Whip Richard J. Durbin of Illinois proposed, tongue planted firmly in cheek, that since Republicans have blocked so many Democratic priorities, perhaps McCain “could come back here and help us.”

It’s not entirely a joke, though. Just last month, McCain missed floor action on a Democratic measure where he could have been their 60th vote — if he had been willing to give it to them. McCain was the only senator who skipped the vote on Reid’s amendment to the economic stimulus package, which would have made low-income seniors and veterans with disabilities eligible for rebate checks. Clinton and Obama both showed up and voted for it, but most Republicans opposed it, and the amendment failed.

That fact of life also means that the eventual Democratic nominee is likely to get at least gentle prodding to show up for the cliffhangers. Reid “would hope and expect that the nominee would be available for close votes,” his spokesman Jim Manley said.

Unlike McCain, neither Obama nor Clinton seems to have worked out a rule of thumb for treating Senate votes as the nominee. “We’d love nothing more than to cross that bridge when we come to it,” says a Clinton spokesman, Philippe Reines; Obama’s campaign did not respond to questions about his plans.

Most political pros, however, say there aren’t many consequences for a nominee who misses Senate votes — and much to lose by showing up. Every day a presidential nominee spends waiting for the roll to be called, “you give up a day in a battleground state,” said David Castagnetti, who was congressional liaison for John Kerry of Massachusetts in 2004.

Lobbyist Steve Elmendorf, who was Kerry's deputy presidential campaign manager, is even blunter. Unless the vote involves an issue that overlaps with the nominee's campaign message, he says, "every day in Washington is kind of a wasted day."