Noonan is (of course) imposing her idea of "the way things should be", onto reality, and while I think her conclusion is okay, I object to her use of the word "failed." Trump didn't "fail" in not changing his style. He chose not to, and the chips will fall where they may. I think part of his objective was in fact to "divide" the party so that those who cannot accept his way, go their separate way. IOW, some division is on purpose, on Trump's part.
Notice absence of failure on the part of anti-Trump forces? They merely "continued." Very easy to see which side of the divide Noonan is on, she's one of those snobs she talks about.