Sen. Ted Cruz of Texas dropped out of the presidential race on Tuesday, sealing Donald Trump's chances of winning the Republican nomination and kindling a firestorm among Republicans on social media.
Some conservatives burned their Republican voter registration cards, calling to mind the protesters who burned their draft cards in opposition to the Vietnam War.
Others shared images of forms changing their party affiliation.
The stream of social media outcry marks a pivotal point in U.S. political history, said historian Dan T. Carter.
"It does reflect, in ways that I never anticipated, the divisions that have existed for a generation within the Republican Party, but that have been papered over by the success of various Republican candidates," Carter said. "Those tensions are now there for all to see."
The outrage sprang up across the gamut of the Republican Party, from conservative writers and strategists to elected officials and rank-and-file voters.
And many angry conservatives took on RNC chairman Reince Priebus, after he tweeted last night that the party should unite around Trump.