Associated Press

Following up on an item from last month, it's hard not to marvel at Rep. David Rivera's (R-Fla.) career. The conservative freshman has been investigated by the FBI, IRS, Miami-Dade Police Department's public corruption unit, the Miami-Dade State Attorney's Office, and Florida Department of Law Enforcement over allegations that he abused his office in the state legislature and repeatedly lied on financial disclosure forms.

But as his re-election race draws closer, Rivera's problems appear to be intensifying.

A key witness in a federal grand jury case involving U.S. Rep. David Rivera is still missing, but she left important evidence behind for investigators: at least four envelopes that had been stuffed with unreported campaign cash.

Ana Alliegro, a Republican political operative, delivered the cash-stuffed envelopes to a Hialeah mail house that sent out fliers in a congressional race against a Rivera political rival, the mail house owner told the FBI.

The FBI has the envelopes to check for fingerprints and handwriting comparisons.

Also in the hands of FBI agents: at least six invoices initially made out to the attention of David Rivera -- all marked paid "cash" -- to cover the mailings for Democratic primary challenger Justin Lamar Sternad, a suspected Rivera straw-man candidate. The congressman demanded that his name be removed from the invoices with Wite-Out, documents and interviews show.

Remember, all of this is real -- it's not from a Carl Hiaasen novel.

The underlying scheme is rather ridiculous. Rivera, fearful of a challenge from Democrat Joe Garcia, allegedly arranged for Justin Sternad to run against Garcia in a Democratic primary. Sternad, whose personal income is about $30,000 a year, somehow managed to spend $43,000 in unreported cash on direct mail.

Did the Republican congressman illegally funnel the money to pay for his opponent's primary race, then clumsily ask that his name be removed from invoices? The FBI seems to think so.

As for the missing witness, she disappeared two weeks ago, and even her lawyer hasn't heard from her, though she was scheduled to talk to prosecutors about her involvement in the scandal just hours before vanishing.

House Majority Leader Eric Cantor (R-Va.) had vowed a "zero tolerance" policy when it comes to misdeeds from congressional Republicans, but has shown no interest in addressing Rivera's multiple and ongoing scandals. I wonder why.