It's kind of fascinating, in a carnivalesque sort of way: the notion of religion as a force alien and dangerous to the American polity, hence to be regarded with fear.
Keller, who is in transition to the job of New York Times op-ed columnist, wants to smoke out religious snakes waiting to bite us. Those Mormons, for example -- Mitt Romney and Jon Huntsman; Rick Perry, with his ties to controversial evangelicals such as John Hagee; Michelle Bachmann, whose views on wifely "submission" might be of interest. And...and...that's pretty much it. No mention of President Barack Obama, who in 20 years of church membership never heard the Rev. Jeremiah Wright declaim on America's wickedness and/or racism.
Presumably, the religious threat we all know ourselves (well, don't we?) to face in America is from people on the right -- never on the left, where tolerant secularism and "progressive" Christianity exude the spirit of democracy.
Keller's inquisitorial exercise is phony baloney, not least because, well, what's Romney or Huntsman going to say -- "Why, yes, Bill, you might as well know now, my campaign is all about the restoration of polygamy"? We can count on Congresswoman Bachmann, no doubt, to respond to Keller, "I can't wait, Bill, for the chance to wiretap every home in America for evidence of wifely non-submissiveness."
More grossly offensive is the liberal/secularist postulate concealed in Keller's scheme of confronting "our scruples about the privacy of faith in public life." We're invited to assume, with Keller, that belief in God, or a Higher Power, if one would rather put it that way, compromises a candidate.
What Keller is proposing, is a cancellation of the Constitution's ban on religious tests for office-holding. The kind of religious test he has in mind subjects candidates to the ordeal of having secular journalists rake over their religious beliefs, judging them mild enough to pass inspection or wild enough to warrant ouster from the race.