A month or so ago, I ran into an investment banker working on the AT&T acquisition of Time Warner at a social gathering.

I won’t say which side of the deal he is on to protect his identity. To break the ice, I came right to the point: I don’t think your deal will get done because President Trump is angry at CNN, I said.

He disagreed and said that AT&T might have to sell CNN but that the deal would go through. I disagreed with his disagreement and we left it at that.

The Justice Department recently sued to block the merger on anti-competitive grounds. AT&T is not giving up.

For decades I covered some of the biggest mergers and acquisitions. And, quite frankly, my days of obsessing over the details of ­deals are over.

But there’s a bigger lesson in this squabble that needs to be addressed.

As a journalist, I’m obliged to defend the First Amendment of the US Constitution, especially the part that says ­Congress shall “make no law … abridging the freedom of speech, or of the press…”

Let’s not quibble over a strict interpretation of that phrase. If you look at the AT&T/Time Warner deal, Congress isn’t doing anything. It’s the Justice Department that is causing problems.

And Justice is part of the Trump administration. And Trump is the guy who has a legitimate gripe against CNN, a cable network that went out of its way to help Hillary Clinton during the election.

The reason CNN was so vehemently and unapologetically pro-Clinton was that everyone figured she was a shoo-in to win. And once that happened, there wouldn’t be anything to worry about.

Then, surprise! Trump won and CNN has become a big problem for its Time Warner parent.