It's said that every senator wakes up in the morning, stares in the mirror, and sees a future president. But Sen. Jeff Flake (R-Ariz.), who is not running for re-election this year, may just look in the mirror and see a future spoiler, someone who mounts a doomed yet vital primary challenge to President Trump. To that idea, I say: Go for it, senator. Flake has become Trump's most incessant critic among elected Republicans, a position he is able to hold by virtue of the fact that he will no longer have to submit himself to the judgment of his party's primary voters.