No sooner had Michael Cohen pleaded guilty than a Democrat lawmaker called for a new investigation to determine if President Donald Trump committed a crime.

Rep. Joaquin Castro accused Trump of being an “unindicted co-conspirator” and called on Congress to launch a probe into possible criminal action by the president.

“For years Michael Cohen was Donald Trump‘s fixer. And today he became America’s fixer, by letting us know in court that we have an unindicted co-conspirator of a federal crime sitting in the Oval Office,” the Texas Democrat said on MSNBC’s “All In” with Chris Hayes on Tuesday, reacting to news that Trump’s former personal lawyer pleaded guilty to charges including tax fraud and campaign-finance violations which he claimed were at Trump’s direction.

“And now the question is what will the US Congress do about that,” Castro, a member of the House Intelligence Committee, said. “I believe that the judiciary committee in both the House and the Senate should open an investigation tomorrow morning.”

But conservative author and radio-TV host Mark Levin provided a hard lesson in how the law actually works, noting how what the president is accused of doing is not even illegal.

“I want to help the law professors, the constitutional experts, the criminal defense lawyers, the former prosecutors and of course the professors and I want to help them understand what the law is,” Levin told Fox News’ Sean Hannity on Tuesday.

The general counsel for the Clinton mob family Lanny Davis, he had his client plead to two counts of criminality that don’t exist,” he added. “It is a plea bargain between a prosecutor and criminal. A criminal who doesn’t want to spend the rest of his life in prison. That is not precedent. That applies only to that specific case. Nobody cites plea bargains for precedent.”

“Just because a prosecutor says that somebody violated a campaign law doesn’t make it so. He is not the judge. He is not the jury. We didn’t adjudicate anything,” Levin argued, using an example to drive home his point.

“Say a candidate had said we owe vendors a whole lot of money. We have had disputes with them. But I want you to go ahead and pay them. I’m a candidate, I don’t want the negative publicity. So he says to the private lawyer, you pay them, I’ll reimburse you, get it done,” Levin explained. “Is that illegal? It’s perfectly legal. Yet according to the prosecution of the Southern District of New York, it’s paid at the direction of the candidate to influence the election. Yes, Mr. Prosecutor, how stupid is your point?”

The former head of the Federal Election Commission, appearing on Levin’s show, also clarified how Cohen’s alleged “hush” payment to porn star Stormy Daniels ahead of the 2016 election is not an in kind contribution to the Trump campaign or a violation of campaign finance law.

“When the FEC wrote the regulation that says what constitutes campaign expenditures and what constitutes personal use, it rejected specifically the idea that a campaign expenditure was anything related to a campaign, and instead says it has to be something that exists only because of the campaign and solely for that reason,” Professor Bradley Smith told Levin Tuesday.

The expenditures alleged by Cohen, Smith explained, are not violations of campaign finance law even though they “might incidentally benefit your campaign,”

“The argument seems to be, and it hasn’t changed,” Levin summed up, “is that, if I spend money to make myself look better, or to take away negative issues in my private life, my business life, my employment life and use my own money, then somehow that is a campaign contribution…which it is not.”