Republican Rob Maness picked up the endorsement of yet another conservative group on Monday in his challenge to Sen. Mary LandrieuMary LandrieuProject Veritas at risk of losing fundraising license in New York, AG warns You want to recall John McCain? Good luck, it will be impossible CNN producer on new O'Keefe video: Voters are 'stupid,' Trump is 'crazy' MORE (D-La.)

The Madison Project endorsed the veteran on Monday, a few weeks after he picked up the support of the Senate Conservatives Fund.

Maness' challenge to Rep. Bill CassidyWilliam (Bill) Morgan CassidyTax bill could fuel push for Medicare, Social Security cuts Collins to vote for GOP tax plan Overnight Tech: Lawmakers want answers on Uber breach | Justices divided in patent case | Tech makes plea for net neutrality on Cyber Monday MORE (R-La.), the establishment pick for the race, for Republican votes could complicate the GOP's chances at defeating Landrieu in 2014. In Louisiana's "jungle primary" system, all candidates are on the same ballot and none crack 50 percent support the top two vote-getters go on to a runoff, a scenario some Republicans worry could boost Landrieu's chances at winning reelection.

In its endorsement, Madison Project spokesman Daniel Horowitz slammed Cassidy as "another trite establishment congressman with no passion for conservatism."

"We learned last cycle from former Reps. Denny Rehberg (R-MT) and Rick Berg (R-ND), we are not going to beat a well-funded savvy Democrat, even in a red state, with a deadbeat establishment politician who stands for nothing and appeals to nobody.  If we don’t step up in support of Rob Maness, and leave the task of defeating Landrieu to the establishment pick, Rep. Bill Cassidy (R-LA), we will not win this seat," he writes.

Rehberg and Berg both lost Senate races considered likely pickups for Republicans last cycle.

Horowitz touted Maness as a possible "citizen legislator" and "antithetical to a career politician like Mary Landrieu."

The conservative has thus far failed to pick up much traction, however, and has had trouble fundraising. The endorsements from Madison Project and other conservative groups could help him turn that around.