The modest crowd, low energy and slapdash feel to Florida Gov. Charlie Crist’s announcement Thursday underscored the needle-threading political exercise ahead for him. By bolting the Republican Party to run for the Senate as an independent—or more specifically, on the “no party affiliation” ballot line—Crist is taking on a low-percentage challenge that few before him have been able to accomplish.

Crist, more than most independent candidates, has reason to worry that his run will be a bust. He is in the process of returning, rather than raising, money. His staff has abandoned him. And he ran a lousy primary race, which presents a fundamental question: what exactly is the rationale for his candidacy?

Unlike Joe Lieberman, who left the Democrats to run on a specific issue — pursuit of victory in the Iraq war, attempting thereby to restore the Scoop Jackson wing of the Democratic Party — Crist’s sole rationale seems to be his own refusal to accept the disgust of Florida’s Republican voters. What does he stand for? Accepting Obama’s stimulus money, not taking a stance on entitlement reform, and maybe not really repealing ObamaCare. Not a compelling platform.

For those who persistently hawk a mushy, conservative-lite agenda, here’s the chance to test-run it. Is there a market for it — a reason to vote for Crist? I doubt it, but Florida voters will tell us.