TRANSCRIPT:
Although the US presidential election isn't until November, the process to choose Republican and Democratic nominees officially kicks off this month.
It's still early days, but some election analysts say the prospect of a Biden-Trump presidential rematch is a real possibility.
If that eventuates, it would be the first presidential rematch since the 1950s - and the seventh in US history.
But Donald Trump's eligibility to run in the presidential race remains a live issue, with the Supreme Court now agreeing to hear his appeal against Colorado removing him from its ballot.
Trump says he is pleased his appeal is being heard.
"And the Republican judges want to go out of their way to be fair and unbiased and even to a point where they hurt you. And I guess it's a different wiring system or something. But all I want is fair. I fought really hard to get three very, very good people. And they're great people, very smart people. And I just hope that they're going to be fair because, you know, the other side plays it rough."
The Colorado Supreme Court on December 19 ruled that Mr Trump must be removed from the 2024 ballot because of his efforts to overturn his 2020 election loss and incitement of the January 6 riot at the US Capitol.
Trump's appeal against that ruling is being fast-tracked ahead of the state's Republican primary on March 5.
But with a caucus on January 15th, Iowa will be the first state to vote for a presidential candidate in the 2024 election.
Days before the ballot, Donald Trump has addressed several hundred supporters at the Sioux Centre in northwest Iowa.
He has told the group about what he believes to be at stake in the campaign.
"You take the ten worst presidents in the history of our country. You can add them up, put them together, and they haven't done the damage that Joe Biden's done to this country. What he's done to this country is unthinkable... This election is your last chance to save America. The battle begins in Iowa on January 15 and Joe Biden's banana republic ends on November 5, 2024."
Joe Biden meanwhile has delivered his first campaign speech of 2024 near Valley Forge, Pennsylvania, where George Washington and the Continental Army spent a winter nearly 250 years ago during the the Revolutionary War.
President Biden has invoked dark moments in the country's history in his speech, including the Revolutionary War, to mark the third anniversary of the deadly insurrection at the US Capitol.
For the president, this election will determine the fate of American democracy, which he says Donald Trump has put under threat.
"Trump's mob wasn't a peaceful protest, it was a violent assault. They were insurrectionists, not patriots. They weren't there to uphold the Constitution. They were there to destroy the Constitution. Trump won't do what an American president must do. He refuses to denounce political violence. So hear me clearly. I'll say what Donald Trump won't. Political violence is never, ever acceptable in the United States political system. Never, never, never. It has no place in a democracy, none."
Washburn University political science professor Bob Beatty says what happens in Iowa will be consequential for the trajectory of the election year.
"Iowans certainly take it very seriously, and there's always the potential for a surprise. I think this year the potential is the surprise could be how close a candidate gets to Donald Trump. I think he will win. The polls can't be put off by this much. But the big question is who comes in second and then how well do they do when they do come in second... And in all the years I've been going to Iowa, I've never seen anything like what Trump is doing. So Trump is campaigning as an incumbent, but with all the advantages of not being in office."
But the Supreme Court appeal ruling will be even more consequential - and is likely to determine his eligibility to run nationwide.
Former federal prosecutor Sarah Krissoff has told PBS NewsHour says the case will be closely watched.
"The Trump team has some good arguments to make, and the Supreme Court is operating without a lot of guidance. There is not a lot of law on these issues and they are free to make new law, and I expect them to do so. They may punt (give) this back to the voters and say this is not the purview of the states to block the former president from the ballot here. I think they may interpret section three of the 14th amendment in such a way to punt this back to the voters."
The Supreme Court case is not the only legal trouble that Donald Trump is dealing with.
Trump is under indictment in Washington DC and Georgia for his efforts to overturn his 2020 election loss, in Florida for his handling of classified documents upon leaving office, and in New York over hush money payments to a porn star ahead of the 2016 election.
In a second New York case, the state's Attorney General is also asking a court to fine Mr Trump, his elder sons and his business over 550 million dollars [[or US $370 million]] in a civil lawsuit.
Letitia James wants Trump banned from doing business in the state where he built his real estate empire, alleging he conducted a myriad of "deceptive schemes" to inflate asset values and conceal facts.
