"I basically told Karl Rove that what he was doing is counter-productive and he needs to stay out of it," said Branstad, recounting a phone call to Rove, the leader of the new Conservative Victory Project.
In the aftermath of last fall's disappointing election outcome for the GOP, party leaders have been focusing on fielding more candidates with broad appeal - and fewer unpredictable ones - but have split bitterly over how to do it, worsening party tensions.
The push was prompted in part by the defeat of Republican Senate candidates Todd Akin in Missouri and Richard Mourdock in Indiana, who lost races the GOP expected to win. The two, who were backed by ultraconservative Tea Party groups, suffered after making controversial comments about rape, and their losses helped kill GOP chances of winning control of the Senate.
The Rove-backed group is planning to raise money and run ads in primary election campaigns to help candidates seen as more attractive to general election voters. The effort is intended to counterbalance fundraising groups that boosted strong conservatives in primary races.
But the targeted effort conflicts with a more diplomatic approach favored by Branstad and other mainstream Republicans wary of offending important officeholders and factions.
There is similar tension about Republican candidates in West Virginia, where the GOP hopes to pick up a seat long held by Democrats, and in Georgia, where Republican Sen. Saxby Chambliss' retirement has set off an internal fight between hard-right conservatives and the GOP establishment.
Branstad, in an interview with the Associated Press, said Rove's plan to use fundraising and negative advertising against suspect Republicans was "a mistake."
"If some outside group that has no connection to Iowa attacks somebody from Iowa, that is not smart," Branstad said.
In the weeks after Iowa Democratic Sen. Tom Harkin announced his retirement, Branstad has used private breakfasts with King and his House colleague Tom Latham to discuss who would be the strongest contender for seat, which has been held by Democrats for more than 30 years.
News of Rove's plans inflamed King, prompting him to issue an angry fundraising appeal in which he declared, "Nobody can bully me out of running."
Representatives of Conservative Victory Project did not immediately respond to requests for comment. But in a New York Times story earlier this month, organization director Steven Law was quoted as saying, "We're concerned about Steve King's Todd Akin problem...All of the things he's said are going to be hung around his neck."
King has strong support among conservatives but also a reputation for provocative statements. During the 2008 presidential campaign, he said a victory by Democrat Barack Obama would be welcomed by terrorists. "If he is elected president, then the Islamist, the al-Qaida, the radical Islamists and their supporters will be dancing in the streets."
King's devout followers, among Iowa's most conservative, were incensed at the news of Rove's group. But so were traditional GOP stalwarts like Richard Schwarm.
"I think that was a total backfire on Rove's part," said Richard Schwarm, a former Iowa Republican Party chairman and longtime Rove friend.