And this is why moderators should not be “fact checking” the presidential candidates on the fly.

During Monday’s debate moderator Lester Holt injected a “fact check” moment during a discussion of “stop and frisk” policies in New York City.

Here is the key exchange:

HOLT: “Stop and frisk” was ruled unconstitutional in New York because it largely singled out black and Hispanic young men.

TRUMP: No, you’re wrong. It went before a judge who was a very against-police judge. It was taken away from her, and our mayor — our new mayor — refused to go forward with the case. They would have won on appeal. If you look at it, throughout the country, there are many places where it’s —

HOLT: The argument is that it’s a form of racial profiling.

TRUMP: No, the argument is that we have to take the guns away from these people that have them and that are bad people that shouldn’t have ’em.

Was “stop and frisk” really ruled unconstitutional? Is it really a form of racial profiling?

The answer is a little bit more nuanced than Holt made it out to be last night.

This morning, my partner Brian Wilson and I interviewed constitutional law professor Alan Dershowitz on WMAL in Washington DC.

Here is the key exchange which begins at 6:10 on the audio player:

DERSHOWITZ: There was a district court judge, Shira Scheindlin, who ruled that the NY stop and frisk, as applied, was unconstitutional. she wrote a hundred and some odd opinion, but it didn’t get to the Supreme Court. The Supreme Court last word on it was a case called Terry v. Ohio many many many many years ago and the Supreme Court held under certain circumstances at least stop and frisk can be constitutional

Look, the interesting thing is how it’s applied. In Massachusetts it was applied in a very effective way with the cooperation of some of the leaders of the African American community and it really helped to disarm gang members in parts of the city where the crime rate was very high. But, if it’s used just as a form of racial profiling then it’s done in a way that probably raises constitutional questions.

But, it’s much more subtle and much more complex and a hard issue to raise in the context of a 2-minute answer in a debate.

O’CONNOR: Probably would have been best for Lester Holt to not wade into “fact checking” on that area…

DERSHOWITZ:  I think you don’t fact check in your question, you fact check after the answer is given, and I think he made a controversial sub-statement which then, Donald Trump responded to, factually, and they both had some truth on their side.

And, in fact, it’s true that Mayor DeBlasio chose to not fight the constitutionality of New York’s version of the policy in a higher court so there is still an open question.

Were North Carolina’s and Texas’ voter ID laws considered constitutional when the lowest courts gave them the seal of approval? No. The constitutionality of those laws were always held open until the left had the answer they’ve waited for from a higher court. Same with Obama’s unilateral amnesty action and the individual mandate embedded in Obamacare.

I hope the remaining moderators learn the “Lester Holt Rule” on fact checking. Stay in your lane and just ask the questions.