WASHINGTON — The Republican Party is once again in the midst of an internal battle, one being led this time by former White House strategist Steve Bannon, threatening to challenge incumbent members of Congress in order to assert a brand of conservatism that has caused headaches for the GOP for the past decade.

It's the latest in a struggle over ideas and direction of the Republican Party and is pitting the former aide to President Donald Trump against establishment leaders like Senate Majority Leader Mitch McConnell and House Speaker Paul Ryan. And it is forcing Trump to choose sides between insurgent candidates praising his name and incumbents being painted as creatures of the swamp he pledged to drain.

The civil war, taking shape more than one year before the 2018 midterm elections, is akin to the tea party wave that helped propel firebrand conservative candidates around the country to win primaries during Barack Obama’s presidency.

In this year's special election to fill the seat of now-Attorney General Jeff Sessions, incumbent GOP Sen. Luther Strange lost the party's primary to Bannon-backed challenger Roy Moore, who is a favorite to win in the general election in December.

Next year, eight Republican senators are up for re-election, including Arizona Sen. Jeff Flake, who is already facing a primary challenge from Kelli Ward, a candidate Bannon campaigned for this past Tuesday.

“It’s an open revolt, and it should be. These people hold you in total contempt,” Bannon said at a rally for Ward in Scottsdale, Ariz.

Mississippi's Roger Wicker could also face a primary threat from a candidate who has met with Bannon. And in a fiery speech delivered to evangelical conservatives last Saturday, the head of Breitbart News named GOP incumbent Sens. John Barrasso of Wyoming, Deb Fischer of Nebraska, Orrin Hatch of Utah and Dean Heller of Nevada as potential future targets. Texas Sen. Ted Cruz is the only one of the eight who has so far completely staved off threats from Bannon’s war.

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“There’s a time and season for everything, and right now it’s a season of war against a GOP establishment,” Bannon said at the Values Voters Summit in Washington, D.C.

Trump, so far, has broken for the establishment. He campaigned for Strange, even as polling showed him well behind Moore. And this week he called Wicker, Fischer and Barrasso to tell them he would back their re-election efforts. The calls came just two days after Trump met with McConnell in the White House where they emerged touting their "outstanding" relationship and McConnell warned of the dangers of backing the fringe of the party.

"Steve is doing what he thinks is the right thing," Trump said Monday. "Some of the people that he may be looking at, I’m going to see if we talk him out of that because frankly they’re great people."

In addition to the incumbents, Bannon’s efforts threaten to also complicate the GOP’s attempt to overtake vulnerable Democratic senators. He is backing candidates in a number of the ten states Trump won that have a Democratic senator up for re-election. Some, like Montana state auditor Matt Rosendale, have received overlapping support from both Bannon and traditional GOP groups. Others are hoping to upend McConnell's picks.

Bannon may also be interested in helping Arizona Rep. Paul Gosar should the state's other senate seat come open, according to multiple sources close to Bannon, even though Sen. John McCain, currently undergoing treatment for brain cancer, has said he has no plans to resign.

Gosar told NBC News he "may explore a Senate run in the unfortunate event of Sen. McCain’s seat vacating.”

"The Steve Bannon primary in Wisconsin is over and Kevin Nicholson has won." Humbled by this huge endorsement. (1/2) — Kevin Nicholson (@KevinMNicholson) October 17, 2017

And as important as recruiting candidates is to Bannon, raising the funds to make them serious challengers is just as key. Bannon has threatened to “cut off the oxygen” to McConnell by recruiting donors who have traditionally supported establishment Republicans but are growing increasingly frustrated by the majority's inability to make good on campaign promises.

Continuing to support Bannon's efforts is the Mercer family, billionaire hedge fund investors who help to bankroll Breitbart News, which is run by Bannon. They’ve given $300,000 to a super PAC supporting Ward and are expected to do more to promote Bannon's 2018 agenda.

It's a position not unfamiliar to Republicans or to McConnell, who has received the brunt of Bannon’s ire towards Washington. At a press conference with Trump at the White House Monday, he compared the current political climate to some of the most infamous tea party backed candidates who flamed out after receiving strong support from the most conservative part of the GOP base.

“The goal here is to win elections in November. Back in 2010 and 2012, we nominated several candidates, Christine O’Donnell, Sharron Angle, Todd Akin, Richard Mourdock. They’re not in the Senate. And the reason for that was they were not able to appeal to a broader electorate in the general election,” McConnell told reporters during a press conference with Trump at the White House on Monday.

McConnell’s list included some of the most notable flops during the height of the tea party movement. Mourdock, who defeated Indiana incumbent Sen. Richard Lugar in a GOP primary, and Akin, who ran against Missouri Democratic Sen. Claire McCaskill, both ran campaigns that became ensnared in controversy after making comments about rape and pregnancy. Akin was leading McCaskill in polling before he said women rarely get pregnant from “legitimate rape.” And two weeks before Election Day, Mourdock said that if a woman gets pregnant from being raped “it is something God intended.”

Christine O’Donnell’s bid for the Delaware seat Joe Biden vacated after becoming vice president became a national punchline after releasing a television ad declaring, “I’m not a witch.” Sharon Angle also failed to defeat one of the GOP’s top targets in 2010, Senate Majority Leader Harry Reid.

"My goal as the leader of the Republican Party in the Senate is to keep us in the majority. The way you do that is not complicated: You have to nominate people who will actually win because winners make policy, losers go home," McConnell said. "We changed the business model in 2014, we nominated people who could win everywhere. We took the majority in the Senate."

Bannon fired back Tuesday in Arizona: “Big Luther Strange and little Bobby Corker are both going home," Bannon said, referring to Tennessee Sen. Bob Corker's decision not to seek re-election in 2018. "These people, Mitch, it’s 2-0. The people of Alabama and the people of Tennessee have already spoken. Your folks are going home. Their folks are going to make policy."

Bannon allies point out that the Republican establishment has backed plenty of unsuccessful candidates themselves, and it’s not up to the party insiders to choose their candidates.

“Mitch McConnell pointed out a number of examples. But in some of those cases, the incumbents that were unseated by the tea party in 2010 and 2012 couldn’t win either,” Joel Pollak, Senior editor-at-large at Breitbart, said on MSNBC on Monday.

Tea party success stories include Florida Sen. Marco Rubio, who defeated Gov. Charlie Crist in a 2010 Senate seat. Nikki Haley also banked on tea party support to defeat a prominent field of South Carolina Republicans to become governor of the Palmetto State in 2010. Deb Fischer, now a potential Bannon target, also relied on tea party support to overcome a huge spending deficit against better financed GOP opponents.

“I don’t think it’s up to Mitch McConnell to decide who can win and who can’t...You can find so many examples of the establishment picking losers,” Pollak said.