Rep. Steve King (R-Iowa) sent out a fundraising email to supporters asking them to help fight back against Karl Rove's "crusade" against him.

"Friend, I'm under attack and I urgently need your help to fight back," King writes in the email. "Since U.S. Senator Tom Harkin announced he will not seek re-election in 2014, rumors have swirled about whether I will run for his seat. I have not made a decision on this matter, but already Karl Rove and his army have launched a crusade against me."

Rove is working with Steven Law, another top establishment GOP operative, on a new super-PAC that aims to keep Republicans they view as unelectable from winning primaries. Law earlier this week called King's penchant for making controversial comments in the past a "Todd Akin problem," a sign the group is likely to oppose him in a primary if he runs.

Former Rep. Todd Akin (R-Mo.), backed by the Tea Party to a primary victory, lost the state's general election for a Senate seat after making a controversial comment about "legitimate rape."

Conservatives in Iowa nationwide have been incensed about the new group — and King is using that anger to rally conservatives to his corner.

"I'm no stranger to outlandish attacks like this. They said I couldn't win in 2012 — the entire political machine was against me — but I soundly defeated my opponent by 8 percentage points. So let me be clear. Nobody can bully me out of running for the U.S. Senate, not even Karl Rove and his hefty war chest," he continues in the email, first posted on The Des Moines Register's website.