Biden chose to make the latest in a series of speeches about that risk - and possibly offer a preview of his 2024 campaign - at an event to honor the late Senator John McCain, a one-time prisoner of war who Trump at one point denounced as "not a war hero."

"And there's something dangerous happening in America now. There's an extremist movement that does not share the basic beliefs in our democracy. The MAGA movement. Not every Republican, not even a majority of Republicans, adhere to the MAGA extremist ideology. I know it because I've been able to work with Republicans my whole career, but there's no question that today's Republican Party is driven and intimidated by MAGA Republican extremists."

Arizona is likely a battleground state in next year's presidential race, and Trump is Biden's likely opponent with a firm lead in recent polls.

In his Thursday speech there, Biden drew attention to Trump's suggestions in recent weeks that the head of the US Joint Chiefs of Staff should be killed and the Department of Justice defunded.

Arizona was also key in Trump's efforts to overturn the results of the 2020 election.

"Democracy means rule of the people, not rule of monarchs, not rule of the money, not rule of the mighty. Regardless of party, that means respecting free and fair elections, accepting the outcome. Win or lose. It means you can't love your country only when you win.

When asked about the president's speech, Trump's campaign responded, "the radical Left Democrats, now led by Crooked Joe Biden, are the greatest threat to democracy the United States of America has ever faced."