More than half of Americans say the nation’s democracy is under major threat, and more than a third say they do not believe that votes cast in the 2022 midterm elections will be counted accurately after a year-long campaign by supporters of former President Trump to undermine the integrity of America’s electoral system.

Elections experts and democracy advocates have been sounding increasingly anxious alarms about the assault on American democracy, but a new poll conducted for Grinnell College by the Iowa-based pollster Ann Selzer finds Trump backers are the most likely to worry about the future of democracy.

The poll, released Wednesday, found 52 percent of adults, 55 percent of likely voters, two-thirds of self-described conservatives and a whopping 76 percent of Trump supporters said American democracy is under major threat.

“There is a general sense in the public that American democracy is in trouble,” said Peter Hanson, a political scientist at Grinnell College and the poll’s director. “That threat is felt particularly acutely by Republicans.”

Concern for the health of American democracy crosses party, geographic and socioeconomic lines: About 4 in 10 supporters of President Biden and a little more than a third of Democratic voters said the same. Older voters are more likely to see a major threat to American democracy than are younger voters, and those in rural areas are more likely to describe a major threat than those in urban or suburban areas.

Just 30 percent of voters say they are very confident that votes cast in the 2022 midterm elections will be counted as voters intended. Thirty-eight percent say they are not too confident or not at all confident that votes will be counted correctly — a number that skyrockets to nearly two-thirds of Republican voters.

Among Biden backers, 89 percent said they were very or somewhat confident that votes in next year’s elections would be counted correctly.

“On the Republican side, rhetoric about a stolen election has metastasized,” Hanson said. “Democratic confidence in the vote has actually gone up by over 10 points despite the fact that there have been all these changes in election laws in Republican states that have gotten attention in the media.”

The results come after a sustained campaign by Trump and his allies to undermine confidence in the results of an election he clearly lost a year ago. Republican legislators and conservative activists have cited unspecified or unproven claims of fraud to advance hundreds of measures aimed at increasing security around elections — or tightening access to the ballot box, in the view of democracy advocates — in recent months.

Republicans have also pursued self-described audits of election results in places like Maricopa County, Arizona, and in Pennsylvania, Wisconsin and Georgia. The Maricopa County results verified official tallies that showed Biden carried the county, and with it Arizona’s electoral votes; a judge in Georgia recently threw out a request to inspect absentee ballots after investigators found no evidence of fraud or deception.

No other investigations have turned up evidence of widespread voter fraud.

But the message that election results are fraudulent, advanced repeatedly and without evidence by a former president stewing in the embarrassment at his own defeat, is sinking in with Republican voters.

“If we don’t solve the Presidential Election Fraud of 2020 (which we have thoroughly and conclusively documented), Republicans will not be voting in ’22 or ’24. It is the single most important thing for Republicans to do,” Trump said, without providing thorough, conclusive or even tangentially related evidence.

Trump’s insistence on sowing doubt has worried Republican strategists and elected officials, who say undermining confidence risks sidelining the voters their party needs to win back control of the House and Senate. They worry about a repeat of January runoff elections in Georgia, when tens of thousands of Republicans who voted in the previous November sat on their hands — and delivered Senate control to Democrats, as Sens. Raphael Warnock (D) and Jon Ossoff (D) beat two incumbent Republicans.

Overall, 9 in 10 Americans say it is very or fairly important that the United States remain a democracy, including 96 percent of Biden backers and 94 percent of Trump supporters.

But few Americans place significant amounts of trust in the federal government: Just 7 percent of voters said they have high degrees of trust in the federal government in Washington, D.C., including only 14 percent of Democrats — in spite of the fact that their party controls the White House and both chambers of Congress.

Hanson said those findings are worrying, and similar to what might be found in fledgling democracies that struggle with stability and even violence around the world.

“Low levels of trust in the government are associated with weak democracies worldwide. That’s why this number concerns us, the fact that it is so terribly low suggests that there may be a more systemic concern, that people are disillusioned with the government’s ability to solve their problems,” he said. “We start to see demands for changes to systems of government, violence, the sort of things that we’ve started to see in the United States.”

The Grinnell College National Poll, conducted Oct. 13-17, surveyed 915 adults over the age of 18, 735 of whom were classified as likely voters. The overall survey carried a margin of error of 3.2 percentage points.