WASHINGTON (AP) — The Supreme Court has ruled unanimously that states can require presidential electors to back their states’ popular vote winner in the Electoral College.

The ruling, just under four months before the 2020 election, leaves in place laws in 32 states and the District of Columbia that bind electors to vote for the popular-vote winner, and electors almost always do so anyway.

So-called faithless electors have not been critical to the outcome of a presidential election, but that could change in a race decided by just a few electoral votes. It takes 270 electoral votes to win the presidency.

A state may instruct “electors that they have no ground for reversing the vote of millions of its citizens,” Justice Elena Kagan wrote in her majority opinion.

The lawyer for the electors who challenged the state rules told The Associated Press that he’s glad the court acted now.

“Obviously, we don’t believe the Court has interpreted the Constitution correctly. But we are happy that we have achieved our primary objective — this uncertainty has been removed. That is progress,” lawyer Lawrence Lessig said.