I once hoped Marco Rubio represented the future of the Republican party, and more important, American conservatism. Now, after his puerile behavior and increasingly vocal — if not slavish or unqualified — support for Donald Trump, that hope is dashed.

I didn’t ignore others’ misgivings about his lack of experience, though arguably it rivaled Ted Cruz’s. I was and am still willing to forgive him for his role in the Gang of Eight; I support a path to citizenship for illegal immigrants and recognize that Rubio was never actually for “open borders.”

But now I admit that those who warned about his poor judgment and apparent opportunism seem to have identified persistent flaws that led to his downfall.

His “robot moment” on the New Hampshire debate stage might have doomed his presidential bid, but the downfall to which I refer didn’t begin until he descended into the mud with Trump. Rubio gave oxygen to Trump’s ridiculous tweets and insulted his person, commenting, among other things, on his — wink – “small hands.” It was embarrassing for everyone — which Rubio admitted, to his credit, but the damage was done.

The childishness hasn’t stopped.