I don't believe that Rick Santorum actually believes this -- he does have a law degree, after all. It's just a plausible narrative that's useful for stirring up the base and getting those all-important direct mail contributions. Maddow did an excellent job of putting him on the spot, however. Via Salon:

On Wednesday night’s episode of “The Rachel Maddow Show,” former Pennsylvania Senator Rick Santorum sat down with Rachel Maddow to discuss same-sex marriage and its impact on America, and though the conversation began cordially — Maddow complimented him on his ability to articulate conservative positions, Santorum complimented her for not resorting to personal attacks — it quickly became heated as they debated the finer points of constitutional law.

Santorum told Maddow that the Supreme Court overstepped its authority with its ruling in Obergefell v. Hodges, saying that the Court “is not the superior branch of government.” He added that Congress could pass a law banning same-sex marriage.

Maddow informed him that it couldn’t, but he insisted that “it’s clear from our founding documents, that the Congress has a right to say what’s constitutional. The president has a right to say what’s constitutional. And that’s part of the dynamic called checks and balances.”

“You’re fundamentally wrong on civics,” Maddow replied. “If there’s a question as to the constitutionality of a law, it gets adjudicated. And the second syllable of that word means it gets decided in the judiciary — the Supreme Court decides whether or not a law is constitutional.”

He continued to insist that Congress could pass a law, so Maddow asked him bluntly, “do you believe Congress could just pass a national ban on same-sex marriage and would it become law?”

“Of course,” he replied. “The Congress could pass anything it wants to pass. The Supreme Court could strike it down again.”

“You want them to pass a moot bill that would just be struck down?” she asked.

“It wouldn’t be moot,” Santorum explained, because the composition of the Court could have changed since it made the current same-sex marriage ruling, or justices could have misgivings about having “misread the tea leaves that are going on in America right now.”

I can see where he might have gotten that idea, what with some of the decisions the Roberts court has made. But he still knows better.

UPDATE: John Amato:

Maddow also confronted Santorum on if being gay is a choice (He said he doesn't know) and his "man on dog' comments. She got him to admit that he wished he never made those comments.

MADDOW: Do you think people choose to -- people can choose to be
heterosexual? You chose --

SANTORUM: All I`m saying, I do know people who have lived a gay
lifestyle and no longer live it.

MADDOW: Do you believe it can be orchestrated? Like you can make a
person --

(CROSSTALK) Advertise

SANTORUM: Again, I don`t spend a whole lot of time thinking about
these things to be very honest.

MADDOW: Well, you`re really very interested in gay rights though. I
mean, you talk about -- you talk about gay rights all the time. That`s the
whole reason you`re a nationally famous figure before you ever decided to
run for president.

SANTORUM: No, not necessarily. What I talk about --

MADDOW: The man on dog thing, when you talk about the moral
equivalent of same sex relationships --

SANTORUM: I didn`t do that.

MADDOW: You did.

SANTORUM: Actually, if you read the quote, and I challenge you to do
it. The reporter actually put the word gay in there. I never said that.

What I said is that the United States Supreme Court changes the
standard to consensual sexual activity as the standard of privacy or
protected under the Constitution.

MADDOW: The question you were answering was about whether or not gay
people should not have sex, because you said you don`t have a problem with
homosexuality. You have a problem with homosexual act. That`s what you
said.

SANTORUM: Go back -- go back to what I was discussing, which was the
Lawrence versus Texas decision. This was all based on a discussion of the
Lawrence versus Texas case.

And what I said was, if people have the right to consensual activity,
then they have the right to and I listed all these different things. Advertise

By the way, if you look at Justice Scalia`s dissent in Lawrence
versus Texas, and, by the way, you looked at Justice White`s majority
opinion in the Bowers decision in the 1986 case, which was the previous
case on this, it`s almost word for word what I said.

The reporter then took us off in a different direction and I said the
things that I said. But the primary purpose of what I was talking about
was changing the legal standard and that that would create a slippery slope
which I think you`re seeing right now, which is -- you know, there are
cases before the courts right now trying to change marriage to allow plural
marriage. And there will be other things that will come around.

And I`m just saying, that the court opened up a Pandora`s box which
at the time, Lawrence versus Texas, I said, we would have --

MADDOW: You`re thinking bestiality?

SANTORUM: I`m saying is that people will make arguments for
consensual activity. That`s what I said.

MADDOW: Including --

SANTORUM: What I said was --

(CROSSTALK)

SANTORUM: I quoted --

MADDOW: Why did you say the word "dog"?

SANTORUM: Because I was quoting -- I was quoting Justice White in
his 1986 decision, and that`s why I was referring to his opinion that that
was the majority opinion at the time. The -- that`s why I discussed it the
way I discussed it.

MADDOW: Do you see how gay people --

(CROSSTALK)

SANTORUM: I wish -- trust me, I wish I had never said that.

MADDOW: You wish you never said it?

SANTORUM: Well, it was -- it was a flippant comment made to a
reporter who was -- well, not being particularly professional in my opinion
in the way she was conducting her interview. But that`s not an excuse for
me. I take responsibility for what I said. What I said --

MADDOW: And you regret it?

SANTORUM: Absolutely. It was a flippant comment that should not
have come out of my mouth. But the substance of what I said, which is what
I referred to. I stand by that. I don`t -- I wish I had not said in a
flippant term that I did. And I know people were offended by it and I wish
you hadn`t said it.