Marco Rubio is a U.S. senator. And he just can’t stand it anymore. “I don’t know that ‘hate’ is the right word,” Rubio said in an interview. “I’m frustrated.” This year, as Rubio runs for president, he has cast the Senate — the very place that cemented him as a national politician — as a place he’s given up on, after less than one term. It’s too slow. Too rule-bound. So Rubio, 44, has decided not to run for his seat again. It’s the White House or bust. “That’s why I’m missing votes. Because I am leaving the Senate. I...