The tension between establishment Republicans and conservative outside groups has reached a fever pitch with the launch of a new Karl Rove-backed project aimed at nominating electable GOP Senate candidates.

The national Republican Party, quite simply, is tired of having less-electable GOP candidates emerge from primaries and -- to their minds -- cost them Senate seats.

But even as the new group is being launched, GOP primaries in a number of key states  already are threatening to test the new project's ability to weed out less-electable candidates and could create battles between more moderate/establishment-friendly candidates and very conservative/outspoken alternatives.

Below, we detail six candidates who could cause problems for the GOP in 2014:

1. Iowa Rep. Steve King: King has been long among the most outspoken conservatives in the House, particularly on immigration and social issues. During the Todd Akin flap last year, King defended Akin and said that he wasn't aware of victims of statutory rape and incest becoming pregnant. He later backed off that position, and it's notable that he recently said he likes the Senate's bipartisan proposal on immigration. That suggests King might be looking to moderate his image, but coming to the middle will be difficult for a guy who has spent much of his career as a bomb-thrower. GOP leaders would much prefer Rep. Tom Latham as their nominee. King said in a recent fundraising e-mail that he won't be "bullied" out of the race by the Rove group, the Conservative Victory Project.

2. Georgia Rep. Paul Broun: Broun, who launched his campaign Wednesday, was tea party before the tea party was a thing, coming out of nowhere to upset an establishment-favored Republican in a 2007 special election (flashback!). Since then, he has been a card-carrying member of the GOP's saying-unhelpful-things caucus. He has dabbled in birtherism and once said, “All that stuff I was taught about evolution, embryology, Big Bang Theory -- all that is lies straight from the pit of hell.” He also has accused the president of upholding the “Soviet constitution" and flat-out labeled him a "socialist." The good news for the GOP establishment is that there are likely to be some other conservative options in the primary, like Reps. Tom Price and/or Jack Kingston, who could attract the support of conservative groups. In addition, the state's runoff law means Broun couldn't simply skate by in a crowded primary field.

Rep. Michele Bachmann (R-Minn.) during a 2012 presidential debate. (Toni Sandys - THE WASHINGTON POST)

3. Minnesota Rep. Michele Bachmann: After her presidential campaign, we're all well aware of Bachmann's very conservative record and style, along with her propensity to say odd things. And polls show that if the former presidential candidate wanted it, she could probably walk to the GOP nomination to face Sen. Al Franken (D) in 2014. Even as she would be a huge favorite in the primary though, the same polls show she would start out with a 14-point deficit against Franken -- bigger than any of Franken's other well-known opponents. Bachmann hasn't said much about a potential Senate run, but running against Franken might be her last, best chance for a promotion.

4. Former Alaska GOP Senate nominee Joe Miller: Miller may not belong on this list, if only because he stands little chance of actually winning a Republican primary to face Sen. Mark Begich (D-Alaska.). After he upset Sen. Lisa Murkowski (R) in a primary in 2010, Miller became hugely unpopular and, even today, is disliked by many of the state's GOP voters. But the fact is that he has won a primary and could conceivably do it again if the primary field -- as expected -- is very crowded. Even in that case, though, conservative groups may not pick Miller over their alternatives.

5. Montana state Rep. Champ Edmunds: The least-known name on this list is one to keep an eye on. The GOP field to face Sen. Max Baucus (D) is expected to be a crowded one, and Edmunds has already signaled his interest and has reserved the Web domain, where he's accepting donations. He's very conservative across the board, including spearheading efforts on illegal immigration, fighting against same-day voter registration and criticizing a Justice Department probe into sexual assault allegations in Missoula. Edmunds is the kind of outspoken conservative who is happy to take on basically any conservative cause and happy to speak bluntly about it. That's not terribly helpful in a Senate campaign, though. Establishment Republicans would much prefer someone like former state senator Corey Stapleton, who announced his campaign this week.

6. Former Louisiana congressman Jeff Landry: The one-term congressman lost in 2012 after having his district merged with the more senior Rep. Charles Boustany (R), but Landry is already talking about taking the next step -- a potential Senate race. Landry won his congressional seat by knocking off the former state House speaker in a primary and then an incumbent Democrat in the general election, so he's shown he can win. During his brief tenure in Congress, Landry was a big ally of the oil and natural gas industry, once holding up a "drilling = jobs" sign at an Obama speech. He also was active in the tea party and at one point said the Obama administration was granting "special status or waivers to Muslims as they go through TSA screenings." One of his final acts as a congressman was to accuse Speaker John Boehner (R-Ohio) of giving in to Obama on the "fiscal cliff" deal.  If he ran, Landry would likely join a field that includes Rep. Bill Cassidy, the current Republican favorite.