“It’s business, it’s conservative and more moderate, too. It’s basically the whole collection,” said Nick Ryan, a veteran GOP operative who has long opposed King. “You’re seeing all segments of the Republican Party really coming together and working together in an effort to defeat King, and that’s something that’s never happened before.”

Though he has a devoted base in his sprawling, northwest Iowa district, King has increasingly become a sore spot for national Republicans as they bleed support from suburbanites and minority communities. His continued membership in the GOP conference — though the party booted him from congressional committees last year — has allowed Democrats to repeatedly yoke him to other Republicans up and down the ballot and forced party leaders to answer for his unending offensive comments.

State Sen. Randy Feenstra — King’s top opponent, who is flush with cash and hundreds of thousands of dollars in outside help — is hammering his message that King is no longer able to deliver because he’s deprived of his committee slots and is a pariah in the party. But he’s also treading lightly on direct criticism of King, wary of alienating the conservative voters who have elected him to Congress every two years since 2002.

Financially, King has never looked more vulnerable. He has not run a single TV ad during the primary and entered the final three weeks of the race with just over $30,000 in the bank. Feenstra has outspent him by a two-to-one ratio and has seen a windfall of independent expenditures on his behalf as public and private polls tightened in the final weeks.

Two super PACs run by a former state House speaker and an ally of Gov. Kim Reynolds have weighed in, with one dropping at least $250,000 on TV ads. The Chamber of Commerce has invested $200,000 on TV ads and text messages, and the political arm of the Republican Main Street Partnership ran $100,000 worth of mailers, calls and online outreach. Feenstra also has the backing of the Republican Jewish Coalition, the National Association of Realtors PAC and the National Right to Life Committee.

“We feel so strongly that this is the first time we’ve ever gone against a sitting member," said Sarah Chamberlain, the president of the Republican Main Street Partnership. "Some of the things he says are just not helpful."

King's comments reflect poorly on the whole GOP, Chamberlain added, comparing him to Todd Akin, the former Missouri congressman whose 2012 Senate campaign collapsed after he said that “legitimate rape” rarely leads to pregnancy. "That caused a problem for the entire Republican Party," she said.

Her group was among the first of the national PACs to spend in the race when it did so in late April. Chamberlain said she received no calls of complaint from House Republicans, which she took as tacit approval. The Chamber of Commerce reported the same silence after it spent in May.

In a rare rebuke of a sitting colleague, five members of the House GOP conference have donated to Feenstra: Reps. Adam Kinzinger (R-Ill.), Paul Mitchell (R-Mich.), Steve Stivers (R-Ohio), Dusty Johnson (R-S.D.) and Will Hurd (R-Texas), who recently launched a group to help diversify the GOP ranks.

“Steve King's divisive and unacceptable rhetoric over the years prevents him from delivering results for Iowans,” Hurd said in a statement to POLITICO. “And it hurts the Republican Party at a time when we should be competing for votes in communities that Democrats like Joe Biden take for granted.”

Hurd and Mitchell are retiring from the House, and Stivers has already had one high-profile run-in with King. When Stivers chaired House Republicans' campaign arm last cycle, he issued a rare, public rebuke of King, just days before the election.

The Iowa political establishment has long dreamed of ousting King and found a new opening after 2018. King was heavily outspent by his Democratic opponent, J.D. Scholten, and won by just 3 points — a shockingly close margin in a rural district that President Donald Trump won by 27 points in 2016. Scholten is running again this year and a rematch with King could be similarly competitive.

In a press conference shortly after Election Day in 2018, Reynolds signaled she had reached a breaking point with King, a co-chair for her campaign. “Steve King needs to make a decision if he wants to represent the people and the values of the 4th District, or do something else,” she said in a comment that likely emboldened donors and operatives looking for permission to conspire against King.

Feenstra entered the race in January 2019, with a campaign team that included some allies of Branstad and Reynolds, shortly before King openly questioned in The New York Times when white nationalism and white supremacism had become negative terms.

The firestorm surrounding King’s remark prompted House Minority Leader Kevin McCarthy to revoke his committee assignments, handing Feenstra and his allies the crux of their argument against the incumbent.

A state Senate leader who helped craft a massive tax cut in the state House, Feenstra has framed his race in terms of effectiveness. And his supporters have followed suit, steering clear of relitigating King's inflammatory comments. The U.S. Chamber of Commerce spot, for example, knocks King for not getting results for Iowa farmers.

“We’re not attacking him for personal reasons or anything,” said Scott Reed, a strategist for the chamber. "It’s about the job he’s doing for the people in the 4th district. He can only vote yea or nay on the floor and has no relevance in the committees.”

And King’s defectors have also emphasized the risk he poses to Trump and Sen. Joni Ernst (R-Iowa), who are counting on his deep-red district to offset the other more competitive regions of the state. In 2018, King barely survived, even as Reynolds carried the seat by 20 points.

“Thousands of people had to make a conscious decision to vote against Steve King and then vote for Gov. Kim Reynolds. But I don’t think that’s a risk you want to take long term — and with Trump on the ballot and Joni on the ballot,” said Bob Vander Plaats, an evangelical leader in the state who is supporting Feenstra. “Trump and Joni will need every vote.”

Trump, who has waded into dozens of congressional races on his Twitter feed, has declined to endorse King or his opponents. Last Friday night, Trump backed two Iowa candidates — state Rep. Ashley Hinson and former Rep. David Young, who are running in the 1st and 3rd districts, respectfully — in a Twitter endorsement spree, but did not mention King's race.

Yet King could still prevail if his loyal legion of followers turn out in high numbers, and he retains strong name ID. He also benefits from a splintered primary field. Three other candidates, who have raised little money, were siphoning away 8 percent of the vote in a recent Public Opinion Strategies poll conducted for an anti-King group that showed Feenstra leading King, 41 percent to 39 percent.

In a televised debate that aired Tuesday, King cast his opponents as "Never Trumpers" who have plotted against him and said McCarthy told him in a phone call last month he would advocate for the restoration of King's committee assignments if he wins reelection. (McCarthy has said he only told King that he could pitch the steering committee on taking him back if he comes back in January.)

"I stood before people when I was first nominated, and I said, ‘If you elect me to this seat, I will use this seat to move the political center to the right,'" King said at the debate, defending his record in Congress. "I’ve kept that promise."

In an election being held mostly by mail, Feenstra and his allies are targeting GOP primary voters that have not voted consistently in the last four primaries, a pattern they believe indicates an openness to voting against King.

And anti-King super PACs have just begun advertising in the Des Moines market to boost Feenstra in the eastern part of the district. His base in Sioux County lies on the state’s western border.

"The momentum is with Sen. Feenstra," said David Kochel, a longtime GOP operative who runs a pro-Feenstra PAC. "That's why you have groups starting to get involved now."