By Jason Lange and Andy Sullivan

WASHINGTON (Reuters) - Two out of three Americans say they are concerned that political violence could follow the Nov. 5 election rematch between Democratic President Joe Biden and his Republican predecessor Donald Trump, a new Reuters/Ipsos poll found.

The survey of 3,934 U.S. adults found widespread worries that the U.S. could see a repeat of the unrest that followed Trump's 2020 election defeat, when the then-president's false claim that his loss was the result of fraud prompted thousands of followers to storm the U.S. Capitol.

Trump is once again laying the groundwork to contest the results should he lose to Biden a second time.

Some 68% percent of respondents to the online poll - including 83% of Democrats and 65% of Republicans - said they agreed with a statement that they were concerned that extremists will resort to violence if they are unhappy with the election outcome.

Overall, 15% of respondents disagreed and 16% were unsure.

In recent interviews, Trump has refused to commit to accepting the election results and at campaign rallies has portrayed Democrats as cheaters.

Outside the New York courtroom where his criminal hush money trial is taking place, fellow Republican officeholders have repeated the falsehood that the 2020 election was stolen from him.

The poll, conducted May 7-14, found that Republicans harbor more distrust in the fairness of U.S. elections than Democrats. Only 47% said they were confident that the results of the November election will be accurate and legitimate, compared with 87% of Democrats who expressed confidence.

The survey has a margin of error of plus or minus 2 percentage points.

Trump's refusal to concede defeat to Biden in 2020 came at the end of a turbulent year marked by the COVID-19 pandemic and widespread racial justice protests.

Though dozens of court cases rejected Trump's claims of fraud, the president and his allies launched a wide-ranging effort to prevent Congress from certifying the results, culminating in the Jan. 6, 2021, attack on the Capitol. Some 140 police officers were injured, one died the next day and four later died by suicide.

More than 1,400 people have been arrested for their involvement in the attack and more than 500 of those have been sentenced to prison, according to the U.S. Justice Department. They include leaders of the extremist Oath Keepers and Proud Boys groups. Trump has characterized those behind bars as "hostages" and has said he may pardon some of them if he returns to the White House.

Trump himself faces criminal charges in Washington and Georgia for allegedly working to overturn his defeat, though those cases are not likely to go to trial before the election. He has pleaded not guilty in both cases and denies wrongdoing.

Recent Reuters reporting has shown that election workers, judges and other public officials have faced a wave of threats and harassment since 2020.

The poll is broadly in line with a similar survey conducted in October 2022, shortly before the midterm congressional elections, which found that 64% of Americans were concerned about extremist violence.

(Reporting by Jason Lange and Andy Sullivan; Editing by Scott Malone and Jonathan Oatis)

Two-thirds in US fear violence could follow election, Reuters/Ipsos poll finds