Maine's top election official has ruled that Donald Trump cannot run for president next year in the state, citing a constitutional insurrection clause.
Secretary of State Shenna Bellows said Mr Trump was not eligible because of his actions leading up to the US Capitol riot in 2021.
Maine now joins Colorado as the two states to ban Mr Trump from the ballot.
The decisions increase pressure on the US Supreme Court to weigh in.
Colorado votes reliably Democratic, however Maine is more politically competitive and would be more significant for Mr Trump - the Republican frontrunner - to lose.
The Trump campaign has already said it will lodge an appeal in the state's courts against the Maine ruling, which won't take effect while the legal process plays out.
Hours after Maine's decision, California - America's most populous state- announced that Mr Trump would remain on the Republican primary ballot there.
Courts in other states, including Michigan and Minnesota, have also recently dismissed efforts to block Mr Trump from running as a candidate.
It is likely that the Supreme Court will make the ultimate decision as to whether Mr Trump can run for president or whether he is ineligible because of a Civil War-era amendment to the US Constitution.
Mrs Bellows' 34-page ruling says Mr Trump must be removed from Maine's Republican primary ballot because of the 14th Amendment- which bans anyone whom has "engaged in insurrection or rebellion" from holding federal office.
In her order, Mrs Bellows, a Democrat, says that Mr Trump "over the course of several months and culminating on January 6, 2021, used a false narrative of election fraud to inflame his supporters and direct them to the Capitol".
She added that his "occasional requests that rioters be peaceful and support law enforcement do not immunize his actions".
Speaking to OceanNewsUK after her ruling, Mrs Bellows said it was her duty to uphold election laws in her state, and that she hoped the "Supreme Court will settle this matter nationwide".
"I'm mindful that no secretary of state has ever deprived a presidential candidate of ballot access based on section three of the 14th Amendment. But I'm also mindful that no presidential candidate has, ever before, engaged in insurrection."
She denied her decision was politically motivated, saying it was "thorough and based on the rule of law".
Mr Trump faces upcoming trials in federal court and in the state of Georgia related to his efforts to overturn his 2020 election loss to Democrat Joe Biden. He has not been charged with inciting insurrection in either case.
His campaign swiftly criticised Mrs Bellows' decision, having previously called for her to recuse herself from the process.
Campaign spokesman Steven Cheung called Mrs Bellows "a hyper-partisan Biden-supporting Democrat" and claimed she was engaging in "election interference".
He added that the campaign would "quickly file a legal objection in state court to prevent this atrocious decision in Maine from taking effect".
Mr Trump's Republican rivals for the presidency also criticised Maine's decision.
Florida governor Ron DeSantis said Maine's ruling "opens up Pandora's Box", suggesting Republican secretaries of state could try to disqualify President Joe Biden over the issue of migrants at the southern border.
"I don't think that this ultimately will be legally sustained by the US Supreme Court. But I do think that this is going to be a constant throughout the election year, where there's going to be different parts of these legal cases that are going to be front and centre," he told Fox News.
Vivek Ramaswamy said "this is what an actual threat to democracy looks like".
Writing on X, formerly Twitter, he restated that he would "withdraw from any state's ballot that ultimately removes Trump from its ballot".
Mr Trump's 2024 presidential candidacy has been challenged in multiple states, on the grounds that the 14th Amendment bans him from holding office.
The 14th amendment was ratified after the American Civil War in order to block Confederate secessionists from returning to power after southern states re-joined the Union.
Colorado's ban was the first instance of the Constitution being used to disqualify a presidential candidate but legal experts say the Colorado ruling will have a tough time standing up when it reaches the conservative-leaning US Supreme Court.
The case to remove Donald Trump from the upcoming Republican primary contest in Maine - part of the process where Republican voters choose their candidate for president - was brought by a handful of former Maine lawmakers who argued that the former president had violated his oath of office.
Former federal prosecutor Joe Moreno told OceanNewsUK he believed there was "no way this holds up".
"It's breathtakingly arrogant for her to unilaterally decide that someone has committed insurrection," Moreno said about Mrs Bellows' ruling.
"This will create a political furore… that's the unfortunate outcome here," he said.
It all leads to a Supreme Court showdown - which Mr Moreno said should take place "rapidly" to stop more states from individually determining Trump's eligibility.
