Trump took to Twitter to attack his fellow Republican, whom he lambasted as "Lyin' Ted" throughout the primary contest.
Cruz was booed roundly during his speech, during which he congratulated, but failed to endorse Trump, who appeared briefly at the convention Wednesday. Cruz also told voters pointedly to "vote your conscience."
"Donald Trump did something no previous nominee has done—he allowed Ted Cruz to speak without his promising to support the nominee. I’ve spoken at every convention since 1992, and I can attest to the fact that no one got near that stage without supporting the nominee. Trump trusted Ted and was rewarded with a betrayal, but the delegates in that arena booed Cruz off the stage and out of Cleveland," Huckabee wrote.
Cruz's words in the speech could be interpreted in a number of different ways, but some saw it as slight against the party's nominee.
"To those listening, please, don’t stay home in November. If you love our country, and love your children as much as I know you do, stand, and speak, and vote your conscience, vote for candidates up and down the ticket who you trust to defend our freedom and to be faithful to the Constitution," Cruz said during the speech.
Cruz was booed by delegates.
"You see this room when people like to make the story and create the dialogue about disunity," Trump Jr. said. "The best unity I saw was everyone booing him off the stage."
Her campaign tweeted "vote your conscience," and included a link to her website.
And Green Party presidential candidate Dr. Jill Stein said: