Really? Is that how you think contracts/pledges work?
If I sign a contractual obligation, and the guy next to me signs one, and then a 3rd guy...but in none of our contracts is there an escape clause based on the other two persons failing to meet their contract's requirements. Yet, somehow in your universe, I just get to decide I'm free because the other fellows failed their obligation.
I don't think so.
Actually, in the situation you describe, that is a failure of consideration/performance by the other parties, and you would no longer be bound. That's basic hornbook law. No "escape clause" is necessary because the contract fails for lack of consideration.
Also, depending on the contract and state law, a "covenant of good faith and fair dealing" may be considered an implied term of many contracts even though it is not expressly contained in the contract. I simply can't get too worked up about candidates "backing out" of such pledges simply because the argument that such promises must be fulfilled
regardless of subsequent events (as opposed to pre-existing factors) is unreasonable. Suppose Trump were indicted for something business related, or was videotaped molesting someone, or it emails were leaked showing that he actually had conspired to throw the election, or it turned out he was extremely ill, or any number of events that could not reasonably have been predicted at the time the pledge was made. Would candidates still be obligated to support a guy under indictment, or who molested someone, etc.? Such promises always come with some implied terms -- namely, that you're not going to do or say something batshit crazy that nobody could have predicted.
To me, that's an excuse for Cruz at least -- nobody would expect someone to support someone who insulted their wife and father. For the other guys, it all depends on how you view what Trump said in March. If he repudiated his obligation at that time, then the other candidates would be justified in doing the same with respect to him.
