There is a line, one that far-right politicians know they must not cross.

Rep. Steve King, R-Iowa, once described undocumented Mexican immigrants as drug mules and likened them to dogs. He supported the end of birthright citizenship and has repeatedly lamented the declining white birth rate. He praised the books and amplified the tweets of neo-Nazis. All along the way, King got the endorsement of Iowa voters in his district, who returned him to Congress every two years since 2003. He received occasional criticism from Republicans insistent that King’s ideas were not their own, while some Democrats said his public comments revealed a bigoted streak, an affinity for white nationalists and an eagerness to make America a less equal place.

But it wasn’t until this week, after King was quoted defending white supremacy, that he found himself booted from the congressional committees where he served. The House overwhelmingly passed a resolution disapproving of his latest racist remarks. All Republicans supported it, as did all Democrats except for one who favored a harsher punishment.

Why was this one moment in the political life of King too much, too far, too outrageous? King’s comment — “White nationalist, white supremacist, Western civilization — how did that language become offensive?” he told The New York Times — was lacking in all plausible deniability and nuance, devoid of the high and low pitch tones calibrated for certain ears, experts say. It was an endorsement of white supremacy in the form of a rhetorical question. And it came at a time when King’s Republican Party is struggling with its political prospects.

“King is not alone in his ideas, not his ideas on immigration, not his ideas about policy,” said Nell Irvin Painter, professor of history at Princeton University and author of “The History of White People.” “But, he is a fairly unusual character, today, in how obvious he is with his racism. The president operates on the side of euphemism, just this side of euphemism, whereas Steve King has used the actual language of white supremacy, the actual words with an endorsement.”

The Morning Rundown Get a head start on the morning's top stories. This site is protected by recaptcha

King has denied sanctioning white supremacy, calling his comments snippets of a longer ill-advised conversation with a reporter that had been misunderstood.

In a statement released Monday night, King called House Republican Leader Kevin McCarthy’s decision to remove him from committees “a political decision that ignores the truth. The truth is as follows: One of my quotes in a New York Times story has been completely mischaracterized."

To Matthew Hughey, associate professor of sociology at the University of Connecticut and author of “The Wrongs of the Right: Language, Race and the Republican Party in the Age of Obama,” there is something inherently hypocritical about the many public rebukes of King. In recent decades, politicians in both major parties have trafficked in the idea that white Americans are biologically or culturally superior while also implying that people of color are dysfunctional, dangerous “threats to white life and livelihood,” Hughey wrote in an email to NBC News.

Republicans have done this more consistently than Democrats for much of the last 50 years, Hughey said. But they don’t own this political tactic, nor the failure to resist the easy temptation of the political victories it can sometimes secure. Racism — provided that it is carefully calibrated and not too overt — sells. It brings “a large segment of U.S. society to the polls and opens their wallets,” Hughey wrote.

But to traffic in those ideas and benefit from them politically, there is that line that can’t be crossed.

“There is a catch: There is an unspoken rule that such racial conjuring must rarely or never manifest as direct advocacy for white supremacy,” Hughey wrote.

Following that rule allows politicians to “advocate for policies that do not outwardly seem racist, but have profoundly white supremacist effects,” Hughey continued. It allows them to “more easily adopt the myth that racism is largely vanquished and a product of bad or ignorant intentions from individual racists rather than a banal and everyday effect of seemingly neutral ideas and stances. In this sense, there is a modern code to evoking racist ideas which Rep. King broke. His language broke the code; it went against the unspoken rule to carefully whisper or dog-whistle racist ideas and policies, rather than scream them from a bullhorn.”

In a country where violence and public displays of enmity motivated by bigotry are climbing, and some say decency is too big a burden to be borne by those who wish to be politically incorrect, the consequences for King are not insignificant, Painter said. While he will continue serving in Congress for now, King lost two committee positions, one on a body with a role in impeachments and high-level investigations.

“What we’ve seen here is an indicator of real but limited progress,” Painter said. “Some Americans may think, ‘How brave do you really have to be to call white supremacy wrong?’ But we have, it seems, reached a point where Republicans themselves see it as in their best interest to take a step beyond condemning the totally obviously racist to the pretty obviously and the plainly obviously racist.”

King’s place in Iowa politics, home of the first presidential primary-season contest, has given him and his ideas a degree of influence. The rebuke King faced this week means that his endorsement may not be sought in 2020 the way it was in 2016, when Sen. Ted Cruz, R-Texas, named King his presidential campaign’s national co-chair. This week, Cruz joined the chorus of those criticizing King, calling his comments “stupid” on NBC’s “Meet the Press.”

Still, King’s previous comments have not stopped voters in his own district from repeatedly returning him to Congress. That, too, has meaning.

Surveys indicate that white support for overtly racist words and ideas has declined over the past half-century, Hughey said. But, during that same period, white support for the policies that perpetuate racial inequality — like tax policies that punish the poor for being needy and heap advantages on the wealthy who make most of their money through investments, not wages or a salary — remain high. That’s what social scientists call the “policy-preference gap.”

“This is perhaps white America’s greatest delusion,” Hughey said. “This embrace of mass self-deception is why many whites — and political parties — are not troubled by King’s racism, in so long as no one calls it ‘racism.’”