President Trump on Monday vowed to challenge a bill approved Sunday by the Nevada legislature that would expand mail-in voting in the state for the November general election.

Trump accused Gov. Steve Sisolak (D), who is expected to sign the bill into law, of using the novel coronavirus to “steal” the election and make it “impossible” for Republicans to win in Nevada.

Nevada is one of the few states won by Democratic nominee Hillary Clinton in 2016 that the Trump campaign thinks could be competitive in 2020. Minnesota and New Hampshire are two other Trump targets.

“In an illegal late night coup, Nevada’s clubhouse Governor made it impossible for Republicans to win the state,” Trump tweeted Monday morning. “Post Office could never handle the Traffic of Mail-In Votes without preparation. Using Covid to steal the state. See you in Court!”

The president’s tweet is part of a growing attack on expanded mail-in voting. Trump has threatened funding to states who are expanding access to mail-in voting during the coronavirus pandemic, claiming mail-in ballots are rife with fraud. Experts say there is no evidence, however, of meaningful election fraud associated with mail-in voting.

Trump last week floated the idea of delaying the election — something he does not have the authority to do — as he continued to sow distrust in mail-in voting. The suggestion inspired widespread pushback from Republicans.   

The Nevada legislature on Sunday afternoon passed Assembly Bill 4, a measure that would guarantee that every active registered voter receives a mail-in ballot in order to vote in the November general election and future elections that are carried out under disaster or emergency declarations that apply to the whole state. Prior to the vote, Trump tweeted that the measure should be met with “immediate litigation.” Sisolak has not yet signed the legislation but is expected to do so.

Nevada is among several states that have moved to expand mail-in voting so that Americans can vote during the pandemic without having to go to the polls, where they could be at risk of contracting or spreading the coronavirus, which has infected more than 4.6 million people and killed more than 154,000 in the United States.

Republicans have taken legal action in order to stop some of the efforts to expand mail-in voting. The Republican National Committee in May sued California to stop Gov. Gavin Newsom (D) from sending mail-in ballots to all voters in the state, arguing that the order would violate eligible citizens’ right to vote and invite election fraud.