Kansas rattles the nation, and the midterms, with its abortion vote.

Voters in deep-red Kansas delivered a loud warning shot to Republicans across the country, signaling that abortion has the potential to energize voters who the G.O.P. had hoped would remain disengaged. Democrats are likely to use the vote to try to build momentum and depict Republicans as out of step with the majority of Americans on the issue.

The vote in Kansas, which resoundingly rejected a ballot referendum that would have removed the right to abortion from the State Constitution, was the first test of Americans’ political attitudes on the issue since the Supreme Court overturned the Roe v. Wade decision. It revealed that from the bluest counties to the reddest ones, abortion rights outran Joseph R. Biden Jr.’s performance in the state in 2020.