So how much did charging taxpayers for a political trip on her private plane and avoiding paying state taxes on that plane hurt Missouri Sen. Claire McCaskill? According to a new survey by the Democratic firm Public Policy Polling, not at all.

In a March PPP poll, 46 percent of Missouri voters approved of the Democrat’s job performance, the same number that approved of her in the survey released on Tuesday. The first-term Senator’s disapproval ticked up 2 points since March, a number within the margin of error.

But the poll didn’t bring only good news for McCaskill, who is a top GOP target next year.

In a matchup with likely Senate contender Rep. Todd Akin (R-Mo.), the race was essentially tied, with McCaskill garnering 46 percent to 45 percent for the six-term Congressman.

The poll showed McCaskill ahead, albeit barely, of both declared Republican candidates in the Senate race. She led former Missouri Treasurer Sarah Steelman by 3 points, a margin that is statistically insignificant, and attorney Ed Martin by a more comfortable 7 points.

McCaskill paid back the money she charged taxpayers for her political trip and paid back taxes on the plane. In an interview with the Associated Press in March, the Senator called her plane issues “a serious, sloppy mistake.”

Responding to the new poll, national Republicans remained bullish on their chances in Missouri.

“The fact is, these results confirm once again that Claire McCaskill is one of the most vulnerable Senators facing re-election in 2012,” National Republican Senatorial Committee Press Secretary Chris Bond said in a statement. “Between her very liberal record and her continued unanswered ethical questions, Senator McCaskill is going to have a very tough time convincing Missourians that she deserves another six years in Washington.”

Democrats trumpeted the news of the poll. “Claire McCaskill is an effective Senator for Missouri and that’s why six weeks of daily attacks from the Republican party didn’t get any traction,” a senior Democratic source in Missouri told Roll Call. “Claire McCaskill is going to have the resources she needs and the will to win this race in 2012.”

PPP used automated telephone interviews to conduct the survey of 555 Missouri voters. The margin of error was 3.9 points.

Roll Call Politics rates the Missouri Senate race a Tossup.