Well in Trump's case there are extenuating circumstances.
Besides the whole purpose of the pledge was to keep Trump from running as a 3rd party candidate if he lost the GOP primaries.
Turns out he hijacked the GOP primaries.
Prove he hijacked the primaries.
Trump didn't hijack the primaries. He is exactly what the crazies want.
It may be better said that Trump completed a 'hostile takeover' of the Republican party. I don't blame any of the responsible republicans for not endorsing him.
Words we will forget during a Trump presidency: civil, dignified, empathetic, thoughtful, contemplative, reasoned.
Words we will learn should there be a Trump presidency: bombastic, reckless, feckless, irrational, boorish, immature.
Dust off your thesaurus, it's gonna be a bumpy night.