This could be the first time in a presidential primary. State Democrat parties in Texas and Florida required that party officials and candidates sign a pledge to support the party's candidate in the general election. Dennis Kucinich refused to sign and took his case to court.
The Virginia Republican party wanted primary voters to sign one. And there was talk in 2004 that attendees at Bush rallies had to sign a pledge of loyalty to be admitted. It's something that's been creeping into US politics for a while now.
There’s something very “commie” about all this. One would *think* that someone who is so high in the polls like Trump would be treated like a gift to the Repub party, but no, they have to treat him like a potential enemy.