What's the highest and best use of a sitting president in an election year when he's not on the ballot himself?
Some would argue it's what the current president is doing Tuesday night in San Francisco -- raising big bucks for his party's candidates. President Obama headed to California on behalf of Sen. Barbara Boxer, one of many Democratic incumbents who are facing very tough re-election campaigns this year.
But Obama has also been showing up to help Democratic candidates actually ask for votes. He campaigned in person for four of them recently -- Creigh Deeds in the Virginia governor's race; Jon Corzine in his re-election campaign for New Jersey governor; Martha Coakley in the Massachusetts Senate race; and Arlen Specter in the Pennsylvania Democratic Senate primary.
All of them lost -- not a good record for presidential coattails.
Another Democrat the president endorsed, Arkansas incumbent Sen. Blanche Lincoln, was forced into a runoff last week. In that case, the White House prudently decided not to have the president campaign for her in person because Arkansas was a state he lost badly in 2008.
Democratic strategist Paul Begala has been through this before. The Democratic president he advised, Bill Clinton, tried hard to help his party hang on to its majorities in Congress in 1994 but failed.
At this point in that election cycle, Clinton had an approval rating of around 51 percent -- a few points higher than Obama's now. But by Election Day in 1994, Clinton's approval was down to around 40 percent, weighing on his party.
Still, Begala says, even unpopular presidents can help their party in a midterm, by framing the choice between the two parties.
"That's what Reagan did," Begala says. "In Reagan's midterm, his job approval was 44, measurably lower than Obama's. But he sustained minimal losses because he defined the choice. He spent every major speech trashing liberal economic policies and saying that that was what the Democrats wanted to go back to. And that's what I'd like to see Obama do."
In reverse, that is. And bashing Republican policies of the past is just what the president plans to do on the campaign trail, says his top political adviser, David Axelrod.
Axelrod describes the November election as a choice, not a referendum.
"It's an easy race to frame: You have a choice between competing visions," Axelrod says. "We've got a Republican Party that hasn't really offered anything new. Their basic posture is let's go back to doing the same things that got us into the crisis in first place -- the same irresponsible policies, the same lack of oversight on Wall Street, the same fiscal policies that brought about these problems."
The president can also rally his party's base by traveling to the right places -- in Obama's case, states where he's still popular. But a president who is very unpopular with certain segments of the electorate can also have the perverse effect of energizing his opponents' base.
Rand Paul, the Republican candidate for Senate in Kentucky, recently told CNN that the GOP was "licking our chops" at running against President Obama.
"Please, please, please bring President Obama to Kentucky," Paul said. "We want him to come and campaign for my opponent. In fact, we'll pay for his plane ticket if President Obama will come down to Kentucky."
But chances are Obama will not come to Kentucky to campaign. He'll do what he can to defeat Paul and other Republicans from safer spots on the national stage -- ones where he has more leverage, and control of a bigger megaphone.