Trump’s court challenges have been unsuccessful at flipping Biden’s wins in battleground states like Georgia and Wisconsin. That leaves convincing Biden electors to ditch him as the President’s last remaining path to a second term. While members of the Electoral College—with the exception of Maine and Nebraska—are pledged to vote for the highest vote getter in their state, most states do nothing to stop them from breaking that pledge.

Biden won 25 states representing 306 electoral votes to Trump’s 25 states with 232 electoral votes. In order to pull off an upset, Trump would need 37 Biden electors to flip and cast “faithless” ballots.

The obstacle for Trump? No presidential candidate has seen more than six electors flip—which happened to James Madison in 1808. And only around 160 faithless ballots have been cast in U.S. history.

In 2016, a total of 10 electors cast faithless ballots, with seven—the highest since 1912—actually counting. Trump lost two electoral votes, and Hillary Clinton lost five. But even that historically high faithless ballot count is still 30 short of what Trump would need this go-around.

And pulling off the feat would be even harder in 2020.

Following the 10 faithless votes in 2016, more states adopted laws that prevent this. According to fairvote.org, a total of 14 states, including Iowa and Michigan, now have laws that will cancel electors’ ballots if they don’t cast it for the statewide winner. Those state laws were upheld by the U.S. Supreme Court in July when it ruled on the Chiafalo v. Washington case. The Supreme Court also deemed state penalties on unfaithful electors as legal.

“In sum, there is zero practical chance that Trump can be reelected by changing the minds of Biden electors in the Electoral College,” wrote Tom Goldstein, publisher of the SCOTUSblog, on Saturday.

Goldstein’s review of state laws finds that 199 Biden electors are already promised to the Democratic nominee by law. That means Trump would have to flip 35% of Biden remaining electors while also not losing any of his own electors.

The President’s best chance at winning enough faithless electors might be to get Republican-controlled state legislatures in states like Wisconsin and Georgia to intervene. The Constitution gives state legislatures the power to determine how electors for their state are chosen, with these elected bodies usually selecting their slates prior to elections. However, some Republicans have discussed asking state legislatures to throw out Democratic slates and put up pro-Trump electors in their place. Currently, no state legislature is actively pursing such an unprecedented move.

In total, 538 electors make up the Electoral College. They’ve never changed the final outcome for President. However, in 1836, they nearly changed the vice president outcome—which electors are also required to vote for. Enough electors flipped from Democratic nominee Richard Johnson that it forced the vice presidential race to the Senate—where he was confirmed.

If none of the vice presidential candidates top 270 electoral votes, the Senate gets to pick. Meanwhile, if neither presidential candidate reaches 270 electoral votes, the vote moves to the House of Representatives. But instead of voting as individual representatives, they’d have to vote as a state—with each state getting one vote. While Democrats have the most House seats, Republicans currently control the most state delegations. The President would be favored in such a scenario, as long as representatives voted along party lines.