Rep. Michael Grimm (R-N.Y.) has secretly been indicted, according to people familiar with the case, following a probe into alleged campaign finance violations. It's a development that threatens to make his reelection bid more challenging.

U.S. Rep. Michael Grimm (R-NY) talks to the media after meeting with House Speaker John Boehner to discuss the relief fund hold up in Congress for Hurricane Sandy victims at the U.S. Capitol in Washington. (REUTERS/Gary Cameron/Files)

In a statement asserting Grimm's innocence, the congressman's attorney said, "When the dust settles, he will be vindicated. Until then, he will continue to serve his constituents with the same dedication and tenacity that has characterized his lifetime of public service as a Member of Congress, Marine Corps combat veteran, and decorated FBI Special Agent."

It's the "Until then" that should worry Grimm when it comes to his political future. Regardless of the outcome, words like "indictment" aren't exactly ideal less than seven months before an election; one, no less, that was already shaping up as potentially close.

Grimm, first elected in 2010, represents New York's 11th district, which encompasses Staten Island and part of Brooklyn. Even before Friday's news broke, he was already facing a competitive reelection race in a district President Obama carried with 52 percent of the vote in 2012. The Cook Report rated his seat as "Lean Republican," which is just one tier safer than "Toss Up."

Grimm was placed in the "Patriot Program" last year, the National Republican Congressional Committee's effort to shore up the most vulnerable House Republicans. The Democratic Congressional Campaign Committee recently named former New York City councilman Domenic Recchia (D) to its "Red to Blue" program, a sign of confidence in his chances.

The filing deadline came and went on Thursday. So it's not as if another Republican can jump in and challenge Grimm. At the end of March, Grimm had about $1.2 million in his campaign account. Recchia had about $1 million.

For many voters in Grimm's district, the inquiry into his campaign finances is not something that will seem out of the blue. In a widely publicized interview with a local TV news outlet after Obama's State of the Union address earlier this year, Grimm threatened a reporter who asked about it. The incident not only brought Grimm negative attention; it also meant the investigation was squarely in the spotlight.

Democrats had already been eyeing Grimm's seat for months. Friday's news should only intensify their interest in competing for his district.