Rubio had arrived at one of the least ambitious moments in Senate history and saw many of his ideas fizzle. Democrats killed his debt-cutting plans. Republicans killed his immigration reform. The two parties actually came together to kill his AGREE Act, a small-bore, hands-across-the-aisle bill that Rubio had designed just to get a win on something.

Now, he’s done. “He hates it,” a longtime friend from Florida said, speaking anonymously to say what Rubio would not.

Which makes for an odd campaign message.

Rubio must convince voters that his decision to leave the Senate — giving up the power he already has — is actually a mark of character, a sign that he is too dedicated to public service to stay.

Rubio is not a quitter, the argument goes.

In fact, that’s precisely why he’s quitting this place.