"That needle has gone over 50 percent," King told The Iowa Republican after initially saying a few weeks ago he was 50-50 on a bid. "Each day that has gone by, on balance, it's more likely, rather than less likely."

King's interest in the race complicates GOP hopes at picking up a seat held by 30 years by Sen. Tom HarkinTom HarkinDistance education: Tumultuous today and yesterday Grassley challenger no stranger to defying odds Clinton ally stands between Sanders and chairmanship dream MORE (D-Iowa), who is retiring. King is a favorite of the GOP base in the state but his hardline conservative views — and some past controversial statements — have Republican strategists worried he won't be able to compete statewide in the swing state. Polls show him in a strong position in the primary but much weaker in the general election than other possible candidates.

That led Karl Rove and Steven Law, the heads of a new super-PAC looking to block Republicans they view as unelectable, to single him out as a likely person they'd try to stop. But King's reaction shows their comments likely backfired on them.

"If I would back up in front of Karl Rove's initiative, that would just empower him, and he would go on state after state, candidate after candidate," King said of Rove. "I don’t think any individual has the wisdom to make those kind of decisions, but I think Iowans together can make those decisions and should. That's the principle. We have to fight this out in the court of public opinion."