If the Democrats can urge people to vote for a candidate not selected in a single primary, and then spend money telling them they have to vote for Harris to save Democracy, then I would think the Republicans can counter with a similar theme.
Some gems from Elon:
"President Trump must win to preserve the Constitution”
“He must win to preserve democracy in America.”
Urging people to vote, saying:
“If they don’t, this will be the last election. That’s my prediction.”
Also urging the crowd to:
“Fight! Fight! Fight!”
My gosh that pesky First Amendment is getting a real workout isn’t it?