Jim Newell has an interesting point on the GOP loyalty pledge:
And though Trump has signed this piece of paper saying he will and won’t do certain things next year, he has not signed any piece of paper requiring him to disavow the unorthodox nationalist, protectionist, tax increase–supporting agenda with which he’s carved his sizable lane. The Republican Party, however, has now committed itself to supporting this agenda, which goes against decades of its own dogma, if Trump is able to pull off the nomination. Most of today’s news has been framed as Trump signs pledge to support eventual nominee. Another way to look at it is Establishment Republican candidates pledge to support Donald Trump. Trump has not pledged to incorporate into his candidacy any of the cheerier tones or traditional Republican policies that the GOP establishment would like to see from him. The Republican Party, though, has agreed to incorporate Trump.
In bringing his politics into the fold, the GOP has also handed Trump a shield just when he might need it. Jeb Bush’s campaign has begun the offensive against Trump’s political past, putting together a montage of Trump over the years stating that he’s pro-choice, a friend and admirer of Hillary Clinton’s, and an advocate for a single-payer health care system—all delivered with the same phony conviction that he wields now to emphasize the opposite. Now, when Bush or whoever else uses these attacks against Trump on the trail or at the next debate, Trump can fire right back: Didn’t you see Reince Priebus come to my office? Didn’t you see me just pledge my support to the Republican nominee? If I were a liberal, why would I do that?
I think this is right. The loyalty oath was a stupid gimmick. Trump bluffed Reince et la. into doing it, with a threat of a third-party run, and now he’s turned it to his advantage.