In New Hampshire, Christie did slightly better with older and better-educated voters, but generally was appealing to the same voters as Trump, which isn't really a surprise. When The Post and ABC News surveyed voters in December, there wasn't a lot of overlap between Christie's and Trump's bases in the more-crowded field, perhaps in part because Christie's support was so shallow.
Christie's campaign was successful in one regard, though. Unlike Bush, opinions of Christie in the eyes of the electorate steadily improved -- not as much as Donald Trump's, but they still ticked upward. He came into 2015 as the one-time front-runner who'd been battered by the bridge scandal. He came out with a net-positive favorability -- still low, but an accomplishment.
What Christie offers Trump, then, isn't voters, and it probably isn't the emotional appeal of a beloved character. As the announcement press conference made clear, Christie will over the short term continue to play the other role he played effectively while a candidate: serial bully toward Marco Rubio. More than that, though, he'll likely also serve as a validator. Not to voters, but to the establishment, which is trying to come to terms with a possible Trump nomination.
Think of it this way.
Chris Christie is a Trump-type (though not quite as Trumpy) who has managed to work with the Republican establishment. He's a conduit between two worlds, the little girl at the TV in Poltergeist. Christie's path to that junction was different than Trump's would be, but he sends a signal to the hand-wringers that Trump has convinced at least one of them that he's legit.
There is nothing about this that hurts Donald Trump. In the wake of the body blows that Rubio landed Thursday night -- which, as with everything in this election, may mean everything or nothing -- Trump now has a serious counter-puncher who might also help give pause to the Republican donors who were otherwise set to rain money on Marco Rubio v. 3.0.
Again: It's impossible to know what happens next. If I'd told you 24 hours ago that Marco Rubio would own Donald Trump in a debate and then Chris Christie would endorse Trump, you'd have been awfully surprised. Who knows what happens in the next 24.