(CNN) Prosecutors have a venerable piece of advice that they often pass along to witnesses. "Always tell the truth," they say, "It's easier to remember."

Of course, the main reason witnesses (and everyone else) should tell the truth is because it's the right thing to do. But the advice from prosecutors gets at a different point. Lies beget more lies, and more lies generate more confusion, and soon the lies cause more trouble than whatever caused the controversy in the first place. This phenomenon is at the heart of President Donald Trump's current legal problems.

Consider the matter of Stephanie Clifford, also known as Stormy Daniels, who is now America's most famous adult film performer. She asserts that she and the President had sex once in 2006. Five years later, a supermarket tabloid recounted their alleged sexual encounter.

And five years after that, at the climax of the 2016 presidential campaign, Michael Cohen, Trump's lawyer and fixer, arranged for a shell corporation to pay Daniels $130,000 for her agreement to remain silent about her relationship with the then-presidential candidate. To this point, the story is seedy but almost certainly legal.

JUST WATCHED Toobin: Trump team lying about Stormy hush money Replay More Videos ... MUST WATCH Toobin: Trump team lying about Stormy hush money 02:32

The lies and omissions started almost immediately. As Rudolph Giuliani, the President's new lawyer, acknowledged Wednesday on Fox News, Daniels was paid because disclosure of her story on the eve of the election would have hurt Trump's chances. And who paid Daniels?

Read More