A federal appeals court ruled Tuesday that three presidential electors from Colorado were unconstitutionally forced to cast their Electoral College votes for Hillary Clinton in 2016.

The 2-1 opinion from the 10th U.S. Circuit Court of Appeals is a victory for so-called “faithless electors,” those who cast an Electoral College vote for a presidential candidate that is not the candidate chosen by a majority of voters in their state.

“Unlike the president’s right to remove subordinate officers under his executive power and duty to take care that the laws and Constitution are faithfully executed, the states have no authority over the electors’ performance of their federal function to select the president and vice president of the United States,” wrote Judge Carolyn McHugh in a lengthy opinion.

The Colorado case involves three Democratic Party electors — Micheal Baca, Polly Baca and Robert Nemanich. After Colorado voted for Clinton in the 2016 race, the three were required under state law to cast their electoral votes for her but wanted to instead vote for John Kasich, a former Republican governor of Ohio, and stop Donald Trump from becoming president.

The scheme was part of a failed national effort to convince Republican electors to vote for Kasich and deny Trump the 270 Electoral College votes needed to become president. The Democratic electors had concerns about foreign interference in the 2016 election aiding Trump.

After voting for Kasich, Michael Baca was replaced by an elector who would vote for Clinton. That led the other two electors to cast their votes for Clinton, despite their desire to vote for Kasich. The three later sued the Colorado Secretary of State’s Office.

A lower court dismissed the lawsuit, finding the trio of electors lacked standing. The 10th Circuit partially reversed that decision Tuesday, ruling Michael Baca had legal grounds for challenging his dismissal, and “the state’s removal of Mr. Baca and nullification of his vote were unconstitutional.”

“This is an incredibly thoughtful decision that could advance substantially our campaign to reform the Electoral College,” said Lawrence Lessig, a Harvard Law professor and lawyer for the electors.

“We know Electoral College contests are going to be closer in the future than they have been in the past; and as they get closer and closer, even a small number of electors could change the results of an election,” Lessig said in a statement Wednesday. “Whether you think that’s a good system or not, we believe it is critical to resolve it before it would decide an election.”

Michael Baca was dismissed by then-Secretary of State Wayne Williams, a Republican, who lost re-election last year to Jena Griswold, a Democrat. On Tuesday, Griswold said the 10th Circuit opinion was concerning.

“This court decision takes power from Colorado voters and sets a dangerous precedent,” Griswold said. “Our nation stands on the principle of one person, one vote. We are reviewing this decision with our attorneys, and will vigorously protect Colorado voters.”

The 10th Circuit returned the case to federal district court for further consideration. But Lessig plans to ask the U.S. Supreme Court to hear the case and issue an opinion by the summer of 2020, before the next presidential election.