A vice-presidential pick is always important, but John McCain confronts a starkly existential choice this year.

Is he running as a Republican or chiefly as a bipartisan deal-maker? Does he have a reasonable shot at victory, or face desperately long odds? Does he want a traditional administration -- with the option of running for re-election -- or something completely different?

The answers will go a long way to determining whether McCain picks Connecticut Sen. Joe Lieberman as his running mate. McCain has left the door open to picking a pro-choice veep candidate, and the pro-choice former Homeland Security Secretary and Pennsylvania Gov. Tom Ridge and Lieberman are reportedly on his short list.

Selecting Ridge, who is at least a Republican, would be a more cautious choice, but also a foolish one. Whatever help he might give in Pennsylvania would be overwhelmed by the disappointment of the evangelical voters who have of late been rallying around McCain. Although Lieberman is more heterodox than Ridge, he makes more sense -- if McCain is willing to follow through on the radical logic of his selection.

Despite being an independent, Lieberman still caucuses with the Democrats in the Senate and has a standard liberal voting record. In 2007, Lieberman and his fellow Connecticut Sen. Chris Dodd -- sometimes talked about as a vice-presidential possibility for Barack Obama -- had identical 70 percent ratings from the liberal Americans for Democratic Action.

Ordinarily, his selection would mean GOP civil war. Never in recent memory has a national ticket had a candidate so at odds with the ticket's party. In 1840, the Whigs put an estranged Democrat, John Tyler, on the ticket with William Harrison -- a clever expedient they regretted when Harrison died and Tyler governed as an unreconstructed Democrat the rest of his term.

To placate Republicans and maximize the political impact of his selection, Lieberman would have to join the ticket as part of a McCain pledge to serve just one term. Both McCain and Lieberman would promise not to run for president in 2012, removing any possibility of Lieberman becoming a successor or putting his imprint on the Republican Party. Their administration would be above electoral politics, a high-minded exercise in competent governance and bipartisan compromise. Continued...