BBC | The US Supreme Court is expected to rule today (Monday) on whether states can use an anti-rebellion constitutional clause to keep Donald Trump off the 2024 ballot.
Colorado used a little-known amendment to the Constitution to remove Trump from the state's Republican primary ballot, citing the January 6 riot.
Fifteen states including Colorado hold their primary elections on Tuesday.
The court said it would post an opinion at 15:00 GMT (6pm).
It did not say which case this would cover but taking the unusual step of giving advance notice has heightened anticipation that it was preparing to rule on the Colorado case.
The Colorado Republican Party had urged the court to issue its ruling before so-called Super Tuesday to clear up uncertainty about Trump's participation.
Oral arguments last month suggested the justices were sceptical about banning Trump from the ballot and they are widely expected to rule in his favour.
In declaring his ineligibility in December for the Republican primary, the Colorado Supreme Court leant on a little-known, Civil War-era constitutional amendment.
Section 3 of the 14th Amendment bars federal, state and military officials who have "engaged in insurrection or rebellion" against the country from holding office again.
Maine and Illinois followed in kicking Trump off the ballot on similar grounds but these were put on hold while his challenge to the Colorado ruling was escalated to the country's top court.
A grassroots campaign to remove him under this obscure amendment gained ground following the storming of the US Capitol by his supporters in 2021.
Groups such as Free Speech For People argued the attempt to delay the peaceful transfer of power on January 6 matched the definition of insurrection as laid out in the amendment.
But critics of the Colorado decision warned the move would rob voters of the chance to deliver their own verdict on Trump returning to the White House.
Some experts were also sceptical of the legal merits, as Trump has never been charged with insurrection related to the Capitol riot.
His lawyers argue his address to supporters before the violence that day is protected by free speech. Trump says his removal amounts to political persecution.
If the Supreme Court clears Trump to compete in Colorado, it would also override challenges brought in other states.
He is expected to sweep the Super Tuesday states to make victory over his Republican rival Nikki Haley all but certain.
The court is taking up a second Trump case, whether he should be immune from prosecution for actions he took as president.
That decision will have far-reaching consequences as he faces several criminal trials.
