Why did Chris Christie have to stand behind Donald Trump like that?

I'm seeing items like "The many pained expressions of Chris Christie standing behind Donald Trump."

Lots of commentary, including lots of mockery. Of course, there's always mockery whenever anything Donald-Trump-related happens, so there's no way to avoid mockery. But, still, why stand there like that?

To me, Christie looked like some sort of body-guard or enforcer, so I'm going to suggest that was the intended message. That is Christie's role in the Trump campaign. Look for more of it. Haters may react: But Christie looked ridiculous! And my response to that would be: Trump has kept you off guard all this time by provoking your ridicule. It's how you are disarmed.