Senator Claire McCaskill of Missouri has a problem--she paid for private plane travel with nearly $76,000 in taxpayer money. Actually, she has two problems--one of those trips, a jaunt across the state to a Democratic event, was entirely political in nature, which violates Congressional ethics rules. In fact, it was reported today that McCaskill really has three problems: after undertaking an audit of that plane, she learned that she owes about $287,000 in back taxes on it.

“I have convinced my husband to sell the damn plane,” McCaskill, who's up for re-election in 2012, told reporters on Monday. “I will not be setting foot on the plane ever again.” But that may not be enough to wash the egg off her face. Here are three reasons this ongoing story will continue to embarrass McCaskill:

1) She's been vocal about the importance of Congressional accountability in the past. McCaskill has embraced her role as a high-profile watchdog; she served two terms as a state auditor for Missouri, and in February, she announced her intention to create a non-partisan auditing body to keep an eye on the Senate. She's also probed spending holes at the Department of Defense in her capacity as a member of the Senate Armed Services Committee. But this business with the private plane doesn't do wonders for her long-cultivated image as a crusader for transparency.

2) The story kept evolving. First there was the reveal of the taxpayer-funded flights, on March 9; then, it came out the next day that one of the flights was for wholly political purposes; now comes the news of the unpaid back taxes. It's worth noting that McCaskill has pledged to return $88,000 to the Treasury Department to compensate for the taxpayer money she used, and that the $287,000 in unpaid taxes were discovered as a result of an audit undertaken by McCaskill's own office. "I'm being held accountable, like I should be," said McCaskill on Monday. "I made this mistake." But it still looks bad, because...

3) The GOP has already turned her own words against her. Check out this ad from the National Republican Senatorial Committee, which features an unfortunate sound bite from McCaskill: "If my walk doesn't match my talk, then shame on me and don't ever vote for me again." (It also features oddly soaring, movie-trailer music, like maybe Harrison Ford is going to make an appearance.)

As the Wire reported a few days ago, McCaskill's own constituents don't seem overly bothered by the unfolding drama. And it may be the case, as Politico's David Cantanese suggests, that her longstanding reputation as a senator of integrity will work to her advantage here. But the analyst Larry Sabato has her listed as "very vulnerable" in the 2012 races. And if Twitter is any indication--"This one ain't goin away Senator," says one user; "Looks like McCaskill's plane is going down!" says another--it's too late to hope this story will slip by unnoticed.