Pictures and videos of the registration cards were shared on social media and at times tweeted directly at Reince Priebus, the chairman of the Republican National Committee, after he called for the party to unite under Trump's campaign.
Instead, some voters responded by literally burning down their ties to the GOP.
This year's election has been particularly contentious between the Republican candidates, which were whittled down from a list of 17 candidates.
The possibility of a contested convention only increased tensions between the remaining candidates, with Trump and Ted Cruz arguing about their wives and Trump dubbing his leading rival "Lyin' Ted."
After losing the Indiana primary Tuesday, Cruz announced he was suspending his campaign, making Trump the presumptive winner of the Republican nomination.
In the last few days the campaigning had turned increasingly combative between Cruz and Trump. On Monday, Trump insinuated Cruz's father might have been involved with the John F. Kennedy assassination.
But after Cruz announced he was suspending his campaign, Trump on Tuesday night called him "one smart guy" and his decision "a very brave thing to do."
But some voters had had enough.
"Adios," one voter said before burning her voter registration. "There goes my card."
Others went online to change their party affiliation, making sure to take a picture of it to share with the chairman of the Republican party, and including hashtags like #NeverTrump.
John Kasich, the governor of Ohio and a distant third in the delegate race, has said he intends to stay in the race.
Several former Republican voters, though, are out.