That pledge is in no way binding and, of course, is an absolutely stupid thing to hold their candidates to. There's literally not a single benefit of requiring that.
You don't think Republican voters will hold their politicians to account for lying?
This is legit funny but it isn't something we can lay at the feet of republicans. Let's say the Governor of Maryland runs in the presidential primaries, they lose to a candidate that they have fundamental issues with, this leads to the governor not endorsing anyone for president, they just choose to stay out of it. Would you, as a Marylander, then not vote for them as governor for their second term, because their party forced them to sign this pledge?
People, of both parties, care about a billion more things than a bullshit loyalty pledge. That's some crap we did in elementary school when we built clubhouses with our friends.