FEDERAL INVESTIGATORS TAKE AN INTEREST IN FLORIDA GOP, RUBIO…. When considering the states where political corruption is common, Florida should rank pretty high. New federal investigations are likely to help solidify that reputation.

Federal law enforcement agencies have launched a criminal investigation into the use of American Express cards issued by the Republican Party of Florida to elected officials and staff, according to sources familiar with the probe.

The U.S. attorney’s office in Tallahassee, the FBI and the Internal Revenue Service are all involved in the probe, which grew out of the state investigation into former House Speaker Ray Sansom. He was indicted on criminal charges that he stashed $6 million in the state budget for an airplane hangar for a friend and campaign donor. […]

Meanwhile, in a separate inquiry, the IRS is also looking at the tax records of at least three former party credit card holders — former Florida House Speaker Marco Rubio, ex-state party chairman Jim Greer and ex-party executive director Delmar Johnson — to determine whether they misused their party credit cards for personal expenses, according to a source familiar with the preliminary inquiry.

A source familiar with the IRS probe told the Miami Herald that investigators are not yet sure whether a full-fledged criminal probe into Rubio’s credit card use is warranted, but there’s enough there to look into it.

While Rubio was legally permitted to use GOP credit cards on party-related expenses, the far-right former House Speaker had charges that included “repairs to the family minivan, grocery bills, plane tickets for his wife, and purchases from retailers ranging from a wine store near his home to Apple’s on-line store.”

Rubio is, of course, currently the leading Republican Senate candidate. As a rule, federal investigations during a political campaign are inconvenient — voters are sometimes skeptical about backing suspected criminals — but for all I know, Florida GOP primary voters may believe that laws have a well-known liberal bias.

That said, headlines such as “Rubio under federal investigation” are the kind of developments that might influence Gov. Charlie Crist’s campaign plans, and for that matter, give hope to Florida Democrats who still think Rep. Kendrick Meek (D) might surprise some people.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.