For months, Roger Stone has gone to bed on Thursday nights expecting to wake up with the feds at his door. “Roger has expected this every Friday since August,” Stone’s friend Michael Caputo, who spoke with Stone last night, told me. So it was not a surprise when F.B.I. agents arrested Stone early this morning at his Fort Lauderdale home. “We all knew it would be Roger Stone Day eventually,” Caputo said. “The bad news is Roger Stone Day is here.”

While not a shock, Stone’s arrest on seven criminal counts—including obstruction, lying to Congress, and witness tampering—has nevertheless sent ripples of fear through Trumpworld. “Trump is very worried,” a longtime Trump confidante told me. Chief among Trump’s fear is the nightmare scenario that Stone flips to avoid years in federal prison and cooperates with Robert Mueller. “I could see Roger flipping pretty quickly,” a Republican close to Trump said.

Emerging from a Florida courthouse, Stone said he will never testify against Trump. But the speculation that Stone could turn on his longtime client is supported by several factors. For one, Stone has a complicated relationship with Trump. The two met in 1979 when Stone was living at Roy Cohn’s Manhattan town house while working as a young staffer on Ronald Reagan’s presidential campaign, and it has rankled Trump that Stone is regarded as his political brain (Stone has claimed he created the “build the wall” slogan). “Stone and Trump are like an old married couple,” the Republican close to Trump explained. “Stone knows Donald isn’t loyal. He calls him ‘Mr. Ingratitude.’”

Stoking Trumpworld’s fear is the fact that Stone is as predictable as an unguided missile. “Donald knows Roger wants to be a martyr,” the longtime Trump confidante said. Right now, Stone has cast himself as a victim of an overzealous prosecutor. His reckless goading of Mueller is the action of a man who seems like he wants to go to jail. “It’s good for his brand,” the confidante said. “It’s pathetic. Why didn’t he just tell the truth?” former Trump adviser and Stone protégé Sam Nunberg told me. But if given the chance to provide a John Dean moment that would ensure his place in the history books, it’s also possible Stone could recast himself as the hero of the Russia probe—while lightening his sentence.

Lastly, some Trump allies fear that Stone’s arrest presages more indictments by the special counsel. The president’s son, Don Jr., has told people he’s worried he could be next, a source briefed on the conversations said. “Underestimating Mueller is a failed tack,” a veteran of the 2016 campaign said.

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