WASHINGTON — The killing of 10 people at a supermarket in Buffalo, N.Y., by what authorities say is an 18-year-old obsessed with racist conspiracy theories has refocused attention on white supremacist ideology, the role social media platforms play in spreading it and the fatal attraction it can offer to alienated young men.

Another issue deserves at least as much public scrutiny — the unwillingness, perhaps inability, of the Republican Party to confront the growth of right-wing violence and the toleration, even outright support, it gets among a significant share of the party’s voters.

A case in point: On Wednesday, the House voted 222 to 203 for a bill to expand the federal government’s resources to investigate, track and respond to domestic terrorism. Only one Republican, Rep. Adam Kinzinger of Illinois, voted in favor. The bill has virtually no chance in the Senate because of GOP opposition.

Republicans, who have blocked similar measures for the last five years, used a familiar argument to justify opposition: The bill unfairly targeted right-wing terrorism, not the left, they said.

“This bill glaringly ignores the persistent domestic terrorism threat from the radical left in this country and instead makes the assumption that it is all on the white and the right,” said Rep. Darrell Issa (R-Bonsall).

That argument flies in the face of increasingly deadly facts.

Right-wing extremists have killed more than 330 people in the U.S. over the last decade, according to statistics compiled by the Anti-Defamation League. That’s 75% of all the deaths caused by political violence in the U.S. Islamic extremists accounted for most of the rest. Left-wing or anarchist violence made up 4% of the deaths.

Last year, terrorists killed 30 people in the U.S. — 28 were victims of right-wing attacks, according to a separate database maintained by the Center for Strategic and International Studies, which has tracked domestic terrorism since 1994.

The last two years had the largest number of attacks since the tracking began, Seth Jones, director of the center’s international security program, told a congressional panel this year.

There’s something awful about toting up numbers of deaths like entries in an ideological accounting spreadsheet, but it’s a sad necessity to highlight a crucial point: There’s no symmetry here, no even balance of problems on both sides.

The U.S. has been hit for most of the last decade by a wave of right-wing violence, much of it committed by white supremacists and aimed at Black and Latino communities. And that wave continues to build.

The pattern resembles a similar violent surge in the early 1990s, which culminated in the bombing of a federal office building in Oklahoma City in 1995 by Timothy McVeigh, a right-wing militant who killed 168 people, including 19 children, in what remains one of the worst terrorist attacks in U.S. history.

In the aftermath of that attack, both parties supported action to find and deter domestic terrorists. The response from Republicans this time around has been denial — at best. At worst, some Republican elected officials have parroted extremist rhetoric.

“The House GOP leadership has enabled white nationalism, white supremacy and antisemitism,” Rep. Liz Cheney of Wyoming, the former third-ranking member of that leadership, who has been exiled for her candor, wrote last week on Twitter.

“History has taught us that what begins with words ends in far worse,” Cheney wrote. Republican leaders “must renounce and reject these views and those who hold them.”

They haven’t, and they probably won’t.

“Candidates want to win elections,” said UCLA political science professor Lynn Vavreck. The “old Republican Party” that formed its identity around limited government and low taxes “just doesn’t exist anymore,” she said.

Divisive issues of race, identity and culture have dominated debate for much of the last decade. “That’s what politics is now, that’s what we’re fighting over these days,” she said.

Unlike issues such as how much to raise or lower taxes, divides over culture and identity do not easily lend themselves to compromise. They’re readily framed as a contest of good versus evil.

Perhaps as a result, even the repudiation of violence, which might seem a simple line to draw, appears risky to many Republican elected officials. They fear to show any sign that they’re anything less than 100% committed to fighting the culture war.

That allows the most radical elements of the party to grow unchecked.

How widely? Since the Jan. 6, 2021, attack on the U.S. Capitol, several organizations have surveyed the public in an effort to find out.

One crucial number: 5%.

That’s the share of American adults who in a survey last year for the University of Chicago’s Project on Security and Threats said they “strongly” agreed that the use of force was justified to restore former President Trump to the White House. A similar share said they strongly believed force may be needed to “save” the “traditional American way of life.”

That’s a small slice of the overall public but a much larger share of the GOP. Even if the vast majority are merely loud talkers, it’s an ominous figure.

Strong believers in political violence, that 5%, are the hardest of the hard core. A larger group of Americans shares a trio of beliefs that Robert Pape, the head of the Chicago project, uses to define what he calls the “insurrectionist movement.” Those beliefs are that the 2020 election was stolen, that President Biden is an illegitimate chief executive, and that force may be at least somewhat justified to remove him.

Based on the survey data, Pape estimates support for the movement at about 8% of the adult population — about 21 million people.

And those people “show up in huge numbers in primaries,” said Vanderbilt University political scientist professor John Geer. Many lawmakers worry far more about angering primary voters than about the general election since the lion’s share of congressional districts aren’t competitive in general elections, Geer said.

“Democracy rests on healthy competition, and right now, we just don’t have it” in most of the country, Geer said. Outsize influence for extremists is one of the consequences.

The insurrection movement centers on Trump and his efforts to overturn his defeat, but it’s tightly bound up with a combination of racism and nativism.

Belief in the “great replacement theory” — the idea that a conspiracy of Jews, Democratic liberals and business leaders are deliberately trying to flood the nation with immigrants to dispossess native-born Americans — strongly predicts support for the movement. So does belief in the QAnon-related theory that the U.S. government is controlled by a secret cabal of pedophiles.

Support for those beliefs goes beyond the hard core of people who openly advocate violence. Nearly 1 in 5 Americans believe two key tenets of replacement theory — that a powerful conspiracy to bring immigrants to the country exists and that native-born Americans are losing economic and political power because of immigration; that soars to about half of viewers of right-wing cable stations OANN and Newsmax and 3 in 10 regular viewers of Fox News.

About 1 in 6 Republicans said that America’s diversity of racial, ethnic and religious groups makes the nation weaker, the Public Religion Research Institute found last year. Just 3% of Democrats feel that way. About 1 in 8 Republicans said they would prefer to have the country made up mostly of people of Western European heritage.

In retrospect, it’s easy to see how the U.S. slipped into its current bitter political divide. In a country rapidly shifting away from a majority-white past, a fight over identity politics may have been inevitable.

It’s a lot harder to see how the country gets out of it. A landslide loss for Republicans might jolt them into reconsidering their path, Geer noted, but that doesn’t seem likely — with inflation high and the public sour on Biden, the GOP almost surely will capture a House majority in this year’s midterm elections.

Eventually, said Vavreck, some new set of issues will come along to supplant the current political divide, but that will probably require a major jolt to the system. “You might have thought a global pandemic would do it, but it didn’t,” she said. “It will have to be something bigger than that.”