You've heard it on TV: What you say can and will be used against you in court.

That also applies to tweets.

Lawyers say what President Trump calls his "unfiltered" tweets already are being used against him in court and in Congress.

"If I'm Donald Trump's lawyer, I have one piece of advice: Stop tweeting at all costs," said legal analyst James Goodnow.

The president's already mired in a case heading to the U.S. Supreme Court, on his executive order banning travelers from six Muslim countries.

Justices will decide whether Trump's ban violates the Constitution.

"Anyone who's seen 'Law & Order' knows that your words can and will be used against you in the court of law," Goodnow said.

"The judges are using those tweets, are using his words to strike down his laws."

This Trump tweet Monday could haunt him in court: "We need a travel ban for certain dangerous countries... not some politically correct term."

Goodnow says the tweet suggests Trump prefers his original Muslim ban.

"That type of religious preference ... shows a preference for a religion which is unconstitutional," Goodnow said.

Attorney George Conway, husband of presidential counselor Kellyanne Conway and former candidate for an administration job, stunned the political world by slamming his wife's boss' tweets.

These tweets may make some people feel better, George Conway said, but they certainly won't help the Trump administration get a Supreme Court majority -- which is what actually matters. Conway mocked Trump by ending "Sad."

"Behind closed doors, a lot of members of the Republican Party are saying the same thing," Goodnow said, "because we've seen what's happened."