I don't think the act itself was that big a deal. I did think it was hilarious that the words copied were those of Mrs. Obama. And I think the bigger deal was how it reflected on Trump's campaign since there are programs that can be used to scan a speech and catch these things, and the Trump campaign didn't even do that much. Also, I don't think it was a question of the Trump team not wishing to throw somebody under the bus. They did what Trump himself does whenever he's told he said this or that. He just denies what he actually said. Time and again he himself just lapses into "no, I didn't say that" mode. And that's what his campaign did. The campaign manager came right out and said it was not plagiarism at all. Christie offered the bizarre rationalization that her speech was only 7% copied. Huh?! Can't even get their act together after the fact. By no means tell the truth and own the mistake, however. Do as Trump does and deny the obvious. Remarkably, that very tactic often works for Trump himself since his supporters could not care less how much Trump lies.
Then, 24 hours later, while it's dying a natural death, the Trump people revive the issue all over again by finally admitting the truth. In several ways, the entire incident shows just how stupid the Trump team really is. Very stupid.
