WASHINGTON (AFP) - One year after the violent assault on the US Capitol, Americans remain deeply concerned about the health of their democracy and about a third say violence against the government can sometimes be justified, according to two polls published Sunday (Jan 2).

The Jan 6 2021 attack on the seat of Congress, led by supporters of former president Donald Trump, was "a harbinger of increasing political violence," and American democracy "is threatened," according to two-thirds of those surveyed for a CBS News poll.

Meanwhile, Americans' "pride" in their democracy has dropped sharply, from 90 per cent in 2002 to 54 per cent now, a Washington Post/University of Maryland survey found.

With the Jan 6 anniversary nearing, the polls offer specific causes for concern: CBS found that 28 per cent of respondents believe force can be used to defend the result of an election, while 34 per cent told The Washington Post that a violent action against government can sometimes be justified - the largest percentage in decades.

The results underscore the seemingly almost irreconcilable views dividing American society, which President Joe Biden - who took office 14 days after the Capitol rioting - has promised to overcome.

On Thursday (Jan 6), he and Vice-President Kamala Harris will deliver remarks to mark the one-year anniversary of the assault by Mr Trump's supporters.

Two-thirds of his supporters continue to believe Mr Trump's baseless charge that Mr Biden is not the legitimately elected president.

Mr Trump had addressed thousands of supporters shortly before the Capitol assault, telling them the election had been "rigged" and that they should "fight like hell."

Some 60 per cent of those polled say Mr Trump bears heavy responsibility for the invasion of the Capitol just as lawmakers were set to certify Mr Biden's victory.

There again, opinion follows partisan lines: 83 per cent of Mr Trump voters placed his level of responsibility at only "some" or "none," the Post survey found.

And 26 per cent of Americans want him to run again in 2024, according to CBS.

A select committee of the House of Representatives has spent months working to establish the roles and responsibility of those who incited or may have organized the protest.

Despite limited cooperation from Mr Trump's inner circle, the panel has conducted more than 300 interviews and collected thousands of documents.

"We have uncovered some things that cause us real concern, things like people trying to... undermine the integrity of our democracy," the panel's chairman, Representative Bennie Thompson, said Sunday on ABC.

"It appeared to be a coordinated effort on the part of a number of people to undermine the election," he said. "It could be people in the executive branch. It could be people in the Department of Defence... and some very wealthy individuals."

He said he would not hesitate to refer any evidence of illegality to the Justice Department.

Ms Liz Cheney, one of only two Republicans on the panel, on Sunday strongly condemned Mr Trump for waiting hours before urging the Capitol rioters to stand down.

He could easily have issued such a call, she told ABC. "He failed to do so. It's hard to imagine a more significant and more serious dereliction of duty."