In a debate this week, Talent accused McCaskill and her husband of not fully paying their taxes, because her husband will not release his tax returns. He also asserted McCaskill had failed to pay taxes on a lakeside condominium and criticized her husband's investment in a Bermuda-based reinsurance firm, a form of tax sheltering the Internal Revenue Service is looking to rein in.

"There is absolutely no tax sheltering that is occurring that is not part of a tax code that Senator Talent embraces," McCaskill countered in the debate. She also accused Republicans of making "smears...against me and my family because they don't have issues to talk about."

The testy debate was a sharp departure from the demeanor of the two candidates in their first two meetings, where the mood was more cordial. The debate took place in Springfield in southwestern Missouri, a Republican stronghold. It also came shortly after Republicans launched a statewide radio ad in which one Talent supporter refers to McCaskill as "a liar and a cheat."

McCaskill's net worth is valued somewhere between $13 million and $30 million , according to public filings. Roll Call, a Capitol Hill newspaper, has said that if elected, McCaskill will be among the top 10 wealthiest members of the Senate.

So far, McCaskill has refused to say how she will handle conflict-of-interest issues if she's elected, including whether she'll excuse herself from some votes or refuse to be on certain committees. Low-income housing, her husband's specialty, is heavily regulated. He also buys and sells tax credits, an industry dependent upon government regulations.

"Before making any determination about what personal decisions she plans to make once elected," McCaskill spokeswoman Adrianne Marsh says, "she must first concentrate on winning on November 7."

One SurveyUSA poll showed that 54 percent of likely voters thought McCaskill won the second debate, while only 32 percent believed Talent had. The latest polls show the race tied within the margin of error.

–Angie C. Marek