The president's presence on the ticket is not expected to help McCaskill in 2012, but the controversy over her jet, which she owns with her husband and a group of investors, threatens to be equally damaging. News first broke earlier this month that the senator had billed taxpayers $79,000 for 89 charter flights, money she eventually paid back to the U.S. Treasury despite insisting she had done nothing wrong. The controversy continued this week when it was revealed she owed nearly $300,000 in back taxes on the plane. McCaskill said it was an oversight and immediately repaid the money - bringing her total payment in back taxes to more than $400,000. But a politician who built her reputation as an outsider focused on reforming government , now looks like part of the corrupt system she once railed against, Duffy writes. Plus, the focus on her private jet could underscore her personal wealth in a working class state. An array of challengers has lined up to face McCaskill in the general election, with a clear front-runner yet to emerge. Former state Treasurer Sarah Steelman and 2010 congressional candidate Ed Martin have declared they are seeking the GOP nomination, while Rep. Todd Akin (R-Mo.) and former RNC co-chair Ann Wagner are also considering bids. None of the candidates may make the A-list, but Duffy said they might not need to be successful. "In truth, Republican strategists don't seem all that happy with the current field," she writes. "None of these candidates are perfect, but it's unclear whether a perfect candidate exists in the GOP's bullpen. The reality is, though, that Republicans might not need a perfect candidate to defeat McCaskill given her problems."