The fate of former President Donald Trump’s attempt to return to the White House is in the hands of the U.S. Supreme Court.

On Thursday, the justices will hear arguments in Trump’s appeal of a Colorado Supreme Court ruling that he is not eligible to run again for president because he violated a provision in the 14th Amendment preventing those who “engaged in insurrection” from holding office.

Many legal observers expect the nation’s highest court will reverse the Colorado ruling rather than remove the leading contender for the Republican presidential nomination from the ballot. But it’s always tricky to try to predict a Supreme Court ruling, and the case against Trump has already broken new legal ground.

“No Person shall be a Senator or Representative in Congress, or elector of President and Vice President, or hold any office, civil or military, under the United States, or under any State, who, having previously taken an oath, as a member of Congress, or as an officer of the United States, or as a member of any State legislature, or as an executive or judicial officer of any State, to support the Constitution of the United States, shall have engaged in insurrection or rebellion against the same, or given aid or comfort to the enemies thereof. But Congress may by a vote of two thirds of each House, remove such disability.”

Trump’s lawyers say this part of the Constitution wasn’t meant to apply to the president. Notice how it specifically mentions electors, senators and representatives, but not the presidency.

It also says those who take an oath to “support” the United States, but the presidential oath doesn’t use that word. Instead, the Constitution requires presidents to say they will “preserve, protect and defend” the Constitution. And finally, Section 3 talks about any other “officer” of the United States, but Trump’s lawyers argue that language is meant to apply to presidential appointees, not the president.

That was enough to convince the Colorado district court judge who initially heard the case. She found that Trump had engaged in insurrection, but also agreed that it wasn’t clear that Section 3 applied to the president. That part of her decision was reversed by the Colorado Supreme Court.

The majority of the state’s highest court wrote: “President Trump asks us to hold that Section 3 disqualifies every oath-breaking insurrectionist except the most powerful one and that it bars oath-breakers from virtually every office, both state and federal, except the highest one in the land.”

Trump’s lawyers contend that the question of who is covered by a rarely used, once obscure clause should be decided by Congress, not unelected judges. They contend that the Jan. 6, 2021, attack on the U.S. Capitol wasn’t an insurrection. They say the attack wasn’t widespread, didn’t involve large amounts of firearms or include other markers of sedition. They say Trump didn’t “engage” in anything that day other than in exercising his protected free speech rights.

Others who have been skeptical of applying Section 3 to Trump have made an argument that the dissenting Colorado Supreme Court justices also found persuasive: The way the court went about finding that Trump violated Section 3 violated the former president’s due process rights. They contend he was entitled to a structured legal process rather than a court in Colorado trying to figure out if the Constitution applied to him.

That gets at the unprecedented nature of the cases. Section 3 has rarely been used after an 1872 congressional amnesty excluded most former Confederates from it. The U.S. Supreme Court has never heard such a case.