Of the races conservative GOP groups have waded into so far, it’s not their crusade against Senate Minority Leader Mitch McConnell that has many national Republicans worried – it’s endorsements in the Louisiana Senate race.

The Senate Conservatives Fund backed retired U.S. Air Force Col. Rob Maness this week over establishment favorite, Rep. Bill Cassidy. Both are trying to unseat Democratic Sen. Mary Landrieu – a vulnerable incumbent sitting in a red state where President Obama only got 40% last year.

But because of the state’s unique election laws, SCF’s endorsement – and whether they engage in the race to hit Cassidy in an effort to boost Maness – has Republicans who have been highly critical of the group’s engagement in primaries sounding off.

The Pelican State doesn’t hold traditional party primaries. Instead, Election Day 2014 functions as an all-party primary. If any candidate tops 50%, they will win outright. But if no one gets a majority, the top two candidates, regardless of party, will advance to a Dec.6, 2014 runoff.

Republicans had hoped to have a one-on-one race against Landrieu, looking to beat her outright on Election Day. But now they fret that any GOP infighting could only boost Landrieu. And while getting 50% outright looks like a longshot for the Democrat, either GOP candidate could limp into a runoff damaged if they’re being hammered by both sides.

“This is a critical seat for Republican hopes to win back the Senate, and it’s stunning that the Senate Conservatives Fund is working to keep it in Harry Reid’s hands,” said GOP strategist Brian Walsh, who served as communications director for the National Republican Senatorial Committee the past two cycles, where several weak candidates emerged from primaries to lose winnable seats.

“[Landrieu] is sitting on a sizeable warchest,” warned Walsh, who has been highly critical of SCF’s strategy in the past. “This is not Texas’ last cycle, and it’s not Mississipi this cycle. This is a very critical seat, and it’s remarkable that this is where they’re looking to make their fight.”

“This would be the biggest gift to Landrieu that anyone could give,” another GOP strategist fretted, fearing that SCF would weigh in to heavily attack Cassidy. “It would ensure her re-election.”

Cassidy has been the favorite to take on Landrieu. With $3.4 million in the bank, he didn’t impress in the last fundraising quarter with just $700,000. Landrieu is sitting on more than $5.7 million in the bank for her race, but both have substantially more than Maness, who raised just $65,000 over the past three months. For his underdog bid, outside help from groups like SCF will be critical.

Cassidy has been criticized as insufficiently conservative by those groups, citing his donation to Landrieu ‘s2002 campaign, which he’s said came before she moved further to the left.

In a fundraising email this week, SCF warned voters to “Beware of Bill Cassidy.”

“Bill Cassidy has rightly been criticized for his Obamacare hypocrisy. Not only did Cassidy propose an Obamacare-lite plan in the state legislature, he’s also tried to take credit for federal grants awarded through the Obamacare program. All of this is making it harder for him to contrast himself with Democrat Mary Landrieu,” SCF Executive Director Matt Hoskins wrote in the email. “To make things even worse, Cassidy previously donated money to Mary Landrieu’s campaign. How does he expect voters to support him over Senator Landrieu when he previously supported her campaign?”

Cassidy has seemed to be working to shore up his right flank in the wake of the challenge, and his vote against the compromise to reopen the government after the 16-day shutdown and raise the debt ceiling was one of the more surprising votes last month.

But Hoskins said that vote was too little, too late and defended the group’s involvement in the race.

“Bill Cassidy is not entitled to be the Republican who faces Mary Landrieu,” said Hoskins. “We have elections so voters can choose who represents them, and we’re confident they will pick Colonel Rob Maness in this race if they’re able to get to know him. That’s why we’re locking arms with the grassroots to help him raise the money he needs to get his message out.”

While there’s still more than a year to go until anyone in Louisiana heads to the ballot box, state observers say that while Landrieu remains highly vulnerable in a state that’s seen significant shifts to the right since she was last re-elected, the infighting in the GOP could be the best thing for her. It’s still unlikely she can top 50% initially, but the two competing Republicans factions only help the Democrat.

“The world has changed in Louisiana–[Landrieu] is going to really have to run a great campaign and have the Republicans or Cassidy help her out a lot to win. There’s just nothing going toward Democrats in any sense of the world,” said nonpartisan Louisiana pollster Bernie Pinsonat.

“There are two things that can re-elect Mary Landrieu– a bad campaign by Cassidy, or the Republicans do what they’re certainly capable of doing, which is re-electing her,” said Pinsonat.