Errol Louis is the host of "Inside City Hall," a nightly political show on NY1, a New York all-news channel. The opinions expressed in this commentary are his own.

While the ex-New York mayor says he'll have a " limited role " and that Robert Mueller's Russia investigation "needs a little push," history shows Trump surrounds himself with loyalists when the end is near. Giuliani's arrival signals that something darker -- perhaps something worse than the Mueller probe -- could be lurking around the corner.

Look no further than the campaign, when Trump expelled the buttoned-up Paul Manafort, an establishment Republican, and went with the far-right Steve Bannon, who let the candidate be himself near the end of what seemed to be a doomed campaign. The same parallel could be drawn with Trump opting to bring Giuliani, a New Yorker of a combative nature, into a team of diplomatic Washington lawyers.

You don't call Rudy Giuliani when things are merely awful: His phone rings when the alternative is complete catastrophe.

He first won election as a Republican mayor in overwhelmingly Democratic New York in 1994 after homicides in the city surpassed a record 2,000 in 1990 and remained high. After 9/11, when he was still the face of the city, Giuliani became for many "America's mayor."

And even before launching his crackdown on street crime, Giuliani was revered (and sometimes reviled) as a crusading US attorney in New York. He took on mobsters, crooked politicians and dishonest Wall Street bankers in the "Greed is good" days of the 1980s. When he spoke with The Washington Post on Thursday, Giuliani played up his service in the Justice Department and ties to Mueller.

"I'm doing it because I hope we can negotiate an end to this for the good of the country and because I have high regard for the president and for Bob Mueller," he told the newspaper.

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Take that as a sign of what's to come. Trump prides himself on loyalty, and few people have been as devoted as Giuliani was during the campaign. He did a marathon tour on the Sunday morning talk shows just days after a leaked "Access Hollywood" tape from 2005 captured Trump making lewd statements about women -- something that kept the rest of his surrogates mum. By contrast, former Trump adviser Bannon previously claimed Chris Christie's wavering support that weekend -- weeks before the campaign -- is why he doesn't work at the White House

So is Trump finally giving Giuliani an administration job after passing him over for the top position at the Justice State and Homeland Security departments? There's a chance he indeed wants Giuliani to negotiate a swift end to the Mueller probe. Trump has looked for the exit sign before when things look bad, and he can surely smell blood in the water after FBI agents raided fixer Michael Cohen's properties last week.

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At least one of the president's soothsayers has reportedly whispered in his ear that Cohen could flip when confronted with the prospect of jail time. His raided files are believed to hold a lot of skeletons for the President.

A mutual pal like Giuliani -- one who stood by him in the darkest hour -- might be Trump's key to ending the Mueller probe legally before it ends his presidency.