Once upon a time, Rudy Giuliani, as the U.S. Attorney for the Southern District of New York, put crooked politicians in jail. This is 30 years ago now, which is a long time, and time, well, it does things to people.

In fact, Giuliani himself delivered a pretty observant remark about time Sunday on CNN, speaking to Dana Bash: “Hey, there are a lot of people with decades of service,” Giuliani said. “Some are good, some bad, and some men get consumed with power, and some begin to lie.”

You can say that again, bub.

Since becoming Donald Trump’s lead lawyer and defender, Giuliani has piled lie on top of lie— statements the Giuliani of the 1980s would have assembled into a devastating dossier that he would have presented with glee to a grand jury.

That Giuliani of 1988—so zealous in pursuit of wrongdoing that he had a daughter wear a wire to record a conversation with her mother, a judge accused by Giuliani of a corrupt act (and acquitted!)—would have been scouring the law books looking for a way to indict the Giuliani of 2018.

I’ve been writing about these people for 30 years now, and this person specifically, Giuliani, for 29—I met him in 1989. I’ve seen a lot of principles tossed out a lot of windows in these three decades, and a number of politicians who became the very thing they once ran against when they were young. But I have never seen a transformation as thorough and as chilling as Rudy’s.

We were never on the same side of the ideological parking lot, and like a lot of people I objected to the gratuitous way he picked fights with political opponents who, funnily enough, were quite often black. But unlike a lot of liberals I had a grudging respect for him.

New York City was a mess when he became mayor in 1994, after running and losing in 1989, and he definitely made the place more livable. For the most part, he hired serious people. Most of the time, I had decent to good relationships with a lot of them—Randy Mastro, Randy Levine, and especially his top aide Peter Powers, who was a terrific public servant and a total gentleman (putting out Rudy’s fires, he had to be).

Then he started to run against Hillary for Senate. This was 1999. The mayor who had very carefully and sometimes showily distanced himself from the national GOP started to embrace it. He needed to raise millions from Republicans all over the country, so he picked some culture-war fights that were out of character or at least his character as mayor of New York City. Then he dropped out of that race after getting a prostate cancer diagnosis, and in the midst of a high profile divorce his then-wife found about from newspaper reports. .

Then, after 9-11, he became America’s mayor. He deserved most of that good press, stupid placement of his bunker notwithstanding, because he did something very surprising. He expressed New Yorkers’ collective grief. You would have expected Rudy to do anger. But he did grief. It was surprising and, apparently, honest. Even an ill-conceived and executed 2008 campaign for presidential didn’t entirely dim his star.

But now? Really—he wants to be out there calling men like James Clapper and John Brennan hacks? (That’s who he was speaking of in the quote to Bash above.) He’s really playing along with this ludicrous and cynical lie of Trump’s about his campaign being spied on?

He’s become a complete caricature of the man he was 30 years ago. But don’t take that to mean he’s a joke. He’s not. As long as he’s out there lying for the lyingest president in the history of the country, he’s a threat to the Constitution.

He said Sunday, also on CNN, that the Mueller investigation is “rigged.” It’s a horribly irresponsible thing for a lawyer to say. The discrediting of the Mueller investigation is also a discrediting of our laws and processes and institutions. Trump has proven repeatedly that he doesn’t care about any long-term damage he does to those, as long as he wins. Hack Republicans like Florida Congressman Matt Graetz don’t care either. I still might have thought that Giuliani would care, a little, and would be more sober and circumspect in his language.

But no. He’s parroting the Trump line all the way. That’s another strange thing about this, too. Giuliani was always certainly his own man. He had a coterie of “Rudy men” around him. Now, for these past two years of his life and seemingly to his last days, Giuliani appears content to be a mere bagman—for a president almost certain to go down in history as one of our worst and perhaps our most lawless.

Why would he do this? Well, one reason might be that Giuliani has his own motivations for discrediting Mueller, since Mueller may well be snooping around into how Giuliani apparently knew that James Comey was going to reopen the Hillary Clinton probe in late October (read Wayne Barrett’s Beast piece from last fall for the background on this).

There may be other reasons we know nothing about. But whatever such facts may be, Giuliani has succumbed to the old adage that he has become what he once beheld.

In 1986, when he was putting crooked pols behind bars, he grilled Bronx Borough President Stanley Friedman on his relationships with Roy Cohn—and Donald Trump. Now, he is acting as Trump’s new Cohn. Except that there’s more at stake now than New York City Parking Violations Bureau contracts.