Leave it to Ben Carson to make what may be at once the most offensive and the smartest single comment of the campaign season so far.

I'm talking about his widely ridiculed appearance on NBC News' Meet the Press in which he said, "I would not advocate that we put a Muslim in charge of this nation. I absolutely would not agree with that." That's obviously the offensive part. Put like that, it sounds like a blanket ban on allowing Muslims to serve as president. Aside from its bigotry, such a ban, if codified in law, would obviously run afoul of Article VI of the U.S. Constitution, which precludes any "religious test" for office.

But then Chuck Todd followed up by asking if Carson would consider voting for a Muslim for Congress. The answer, in which Carson pivoted to a different point, has been much less widely reported. That's too bad, because when his original statement is combined with the nuance he added in response to the follow-up question, we're left with a sensible, even laudable position on a crucially important topic.

Here's what Carson went on to say:

Congress is a different story, but it depends on who that Muslim is and what their policies are... And, you know, if there's somebody who's of any faith, but they say things, and their life has been consistent with things that will elevate this nation and make it possible for everybody to succeed, and bring peace and harmony, then I'm with them. [NBC News]

That's a little vague, so let me unpack what I take to be Carson's point.

Religion and God are immensely important matters. Of course a candidate's faith matters. Of course a thoughtful, informed citizen should weigh the religious beliefs of any man or woman running for office. That includes Congress, but it's especially true when that office is the presidency — the most powerful one in the country (and the world) by far.

But at the same time, blunt sectarian designations (Catholic, Protestant, Jew, Mormon, Muslim, atheist) can't serve as a shortcut or a stand-in for judgment, because each faith community is enormously diverse. We therefore need to educate ourselves about precisely what each candidate affirms from his or her faith community, and weigh that information against what we take to be the bedrock requirements for exercising citizenship on the highest level (serving as commander-in-chief and head of the executive branch of government).

As I've argued at some length on other occasions, that is exactly the kind of thinking — and precisely the kind of informal religious test — we need.

Now, it should be clear that questioning the religious beliefs of candidates is not the same as administering a constitutionally precluded religious test. Article VI forbids a legal religious test, one that either requires officeholders to be members of a specific church or bans all members of a specific church from holding office. It's safe to say that no one has and no one will be advocating that we institute anything like such a test. (Actually, I take that back. I wouldn't really be surprised if Donald Trump came out in favor of just such a constitutionally precluded test. Hell, he'd probably boast that he could get it enacted without a constitutional amendment on the same afternoon he scraps the Fourteenth Amendment by fiat.)

All I'm suggesting is that we be as informed as possible in deciding how to vote. The fact is that in the abstract every faith community affirms certain beliefs that stand in considerable tension with, and may even flatly contradict, liberal democratic norms.

At the same time, far from every member of every faith community accepts its most illiberal elements. Some reject them all. (We usually call them theological liberals.) Others affirm all of the community's most illiberal beliefs and practices, and may even, like ISIS, add several new ones. (We call these people fundamentalist, ultraorthodox, or fanatical.) Still others — perhaps most others — mix some aspects of liberalism and orthodoxy.

The kind of informal religious test we need would obviously have no issues with the first group, and it would just as obviously counsel very strongly against giving any political power to the second. Those cases are easy. It's the third category that requires the most thinking and judging.

There are two ways to respond to the third group.

The first, more awkward option is to identify the troubling religious beliefs of a candidate's faith community and ask the candidate straight out which she affirms and which she rejects.

The second and far better option is to get the candidate to confirm that he would take the oath of office — and mean it. In swearing that he would "preserve, protect, and defend the Constitution of the United States," the would-be president affirms that he would treat the nation's fundamental law as the highest or ultimate law in all circumstances — even if and when he sensed a tension or conflict between the Constitution and his personal faith. As long as a candidate publicly pledges to put his faith aside in the case of a direct conflict between it and the duties of his office, he passes the religious test.

And that brings us back to Carson's comments — both to what was smart about them, and what was offensive.

Carson's first, widely decried comment about how we shouldn't "put a Muslim in charge of this nation" is a perfect example of how not to administer an informal religious test — because it treats all Muslim-American citizens as if they uniformly affirm illiberal views. Whether Carson meant to imply that a Muslim president would inevitably reveal himself upon taking office to be a covert ISIS operative or merely seek to impose Sharia law on the nation, the insinuation was both insulting and ignorant.

But in his later statement, Carson gestured toward something far more thoughtful: What matters is what a candidate says and how she lives her life. If she's used her actions and words to elevate the nation, encourage success, and foster peace and harmony, then it shouldn't really matter what faith community she belongs to.

Exactly right.

And if doubts persist, there's always the oath of office to ensure the candidate has passed the test.