WASHINGTON — Paul Manafort is going to jail.

Special counsel Robert Mueller's office convinced a federal judge on Friday to revoke the bail of President Donald Trump's former campaign chief after he was accused of witness tampering.

"I cannot turn a blind eye to this," Judge Amy Berman Jackson said in a Washington courtroom, explaining that she could not just release Manafort with more restrictions.

"This isn’t middle school, I can’t take your phone," Jackson said.

Manafort, 69, did not appear to react to the ruling beyond a nod to his attorney. He was immediately taken into custody and walked into a hallway behind the courtroom. He gave a quick wave to his wife as he disappeared from sight.

He will remain in pretrial detention until a trial in September on charges that include conspiracy and money laundering; he also faces a separate trial in Virginia.

The move drastically ratchets up pressure on Manafort as Mueller continues to investigate whether there was collusion between the Trump campaign and Russians to interfere in the 2016 presidential election. His ex-business partner, Rick Gates, who was indicted with him in October, has already pleaded guilty and agreed to cooperate.

After Jackson's ruling, Trump tweeted that Manafort got a "tough sentence" — though he hasn't actually been sentenced for anything — and tried to downplay his involvement with the campaign.

"Like Manafort has nothing to do with our campaign," the president told reporters at the White House before the hearing.

"You know, Paul Manafort worked for me for a very short period of time. He worked for Ronald Reagan. He worked for Bob Dole. He worked for John McCain, or his firm did. He worked for many other Republicans. He worked for me, what, 49 days or something. Very short period of time."

In fact, Manafort worked for the Trump campaign for 144 days. He joined the campaign in March 2016, became chair in May and resigned in August 2016.

Before Friday, Manafort had been largely confined to his home, tethered to two GPS ankle monitors while awaiting a trial set for the early fall.

But prosecutors made a new bid to toss him behind bars after uncovering evidence that allegedly shows that he and a Russian associate, Konstantin Kilimnik, used encrypted messages to reach out to two witnesses — one of whom said it was an attempt to "suborn perjury."

In court filings, defense lawyers accused Mueller's office of "heavy-handed gamesmanship" and argued text messages and an 84-second phone call were "the thinnest of evidence."

At Friday's hearing, the judge said she was not revoking Manafort's bail as punishment but because his attempts to contact witnesses constituted a danger to the court's integrity.

"I have no appetite for this," she said.

Manafort attorney Richard Westling asked the court for a stay pending appeal but it was immediately denied by Jackson.

Jackson had previously chastised Manafort about breaking the rules: In December, she warned him that work he did on an op-ed in a Ukrainian newspaper could be viewed as an attempt to circumvent a gag order in the case.

Before the bail ruling, Manafort was arraigned on two obstruction charges tied to the alleged witness-tampering. He pleaded not guilty to both counts. Kilimnik, who has also been charged with obstruction, was not at the hearing.

The obstruction charges were contained in a third superseding indictment filed by Mueller a week ago. Manafort now faces dozens of felony counts in two jurisdictions, mostly linked to his lucrative lobby work in Ukraine.

None of the filed charges relate to meddling in the 2016 election, but a guilty plea from Manafort would be an enormous coup for Mueller, who has secured indictments against 20 people — from former national security adviser Michael Flynn to employees of a Russian troll farm.