Landrieu is likely to face a tough race in the conservative, increasingly Republican state.

A number of House Republicans are thought to be interested in the seat. Rep. Bill Cassidy (R-La.) has $2 million in the bank, by far the most in the House delegation. Rep. John FlemingJohn FlemingFreedom Caucus member to bring up bill on impeaching IRS chief GOP seeks to make it 52 Louisiana Senate race heads to runoff MORE (R-La.) has $480,000 cash on hand but is carrying nearly $250,000 in debt, while Rep. Charles BoustanyCharles BoustanyClay Higgins wins La. House seat Louisiana dishes last serving of political gumbo We can't let tax extenders obstruct comprehensive reform MORE (R-La.), who faced a tough race from former Rep. Jeff Landry (R-La.), has $190,000 in the bank. Landry, a Tea Party favorite who hasn't ruled out the race, has just $67,000 left, with $22,000 in debt.

While a contested primary often benefits the other party, because of Louisiana's unusual election rules all candidates run on one ballot in the November election, and the top two vote-getters then have a runoff in December, making the race more expensive for all candidates and putting a premium on early fundraising for the candidates.