WASHINGTON — Paul Manafort, President Donald Trump’s former campaign chairman, was jailed Friday after a federal judge decided that his messages to former colleagues represented an attempt to tamper with witnesses in the special counsel investigation.

U.S. District Judge Amy Berman Jackson said Manafort’s behavior showed he was “a harm to the administration of justice and the integrity of the court system.”

“You have abused the trust placed in you,” she told Manafort, adding that sending him to jail until his trial was “an extraordinarily difficult decision.”

After the ruling, one of Manafort’s lawyers jumped to his feet and asked to delay the imprisonment while they appealed, but Jackson refused.

As Manafort was taken into custody, he turned back and caught the eye of his wife in the packed courtroom, raising his hand and giving her a firm smile.

The decision to revoke his bail was a severe blow to Manafort, who spent years at the highest levels of Republican politics before making millions as a consultant for some of the world’s least-savory dictators. He re-entered the spotlight by guiding Trump’s campaign during the contentious Republican National Convention two years ago, only to be forced out amid controversy over his previous work on behalf of Ukraine’s pro-Russian government.

Manafort has been under house arrest since last October, when he was first indicted over financial crimes unrelated to the campaign, including tax evasion and bank fraud. Unless he beats the charges he’s facing in two separate trials this year, the 69-year-old could remain behind bars for the rest of his life.

Harry Litman, a former federal prosecutor and law professor at the University of California, said Manafort is facing “maximum pressure” to cut a deal with special counsel Robert Mueller, who has been investigating Russian interference with the presidential election. Because the charges against Manafort have been so well documented, Litman said, his risk of losing at trial is high, and if convicted, “absent cooperation, he will never get out of prison.”

“So that means this is the first day of the rest of his life,” he said. “The first crappy meal. The first regimented schedule. The first of a series of indignities.”

Shortly before Friday’s hearing began, Trump tried to distance himself from his former campaign chief. “Paul Manafort worked for me for a very short period of time,” Trump told reporters.

Manafort, in fact, was part of the campaign for several months and played a leading role in securing support for Trump from party delegates.

After the judge’s ruling, the president came to Manafort’s defense, calling the decision “very unfair!”

“Wow, what a tough sentence for Paul Manafort, who has represented Ronald Reagan, Bob Dole and many other top political people and campaigns,” the president tweeted. “Didn’t know Manafort was the head of the Mob. What about Comey and Crooked Hillary and all of the others? Very unfair!”

Trump’s lawyer, former New York City mayor Rudy Giuliani, was more explicit — raising the possibility of a presidential pardon in an interview with the New York Daily News.

“When the whole thing is over, things might get cleaned up with some presidential pardons,” said Giuliani, a former U.S. attorney in Manhattan. “You put a guy in jail if he’s trying to kill witnesses, not just talking to witnesses.”

Prosecutors first revealed the witness tampering allegations against Manafort this month. In a court filing, they said Manafort and his business partner, Konstantin Kilimnik, reached out to two public relations professionals to provide them with false information about the Ukrainian lobbying.

In encrypted messages, Manafort and Kilimnik told them that the advocacy only took place in Europe, prosecutors said. The location matters because Manafort has been charged with violating a federal law that requires agents of a foreign government to register if they do work within the United States.

“We should talk,” Manafort wrote in one of the messages, according to a court filing from prosecutors.

The recipient of the messages provided their content to prosecutors because he was concerned that he was being asked by Manafort to provide false testimony, the court filing said.

The outreach began after Richard Gates, another former Manafort business partner and Trump campaign aide, pleaded guilty in February to charges of conspiracy and lying to federal agents. Gates is cooperating with the special counsel’s investigation.

Manafort and Kilimnik, whom prosecutors accuse of having ties to Russian intelligence, were indicted last week on charges of obstruction of justice and conspiracy to obstruct justice.

Manafort pleaded not guilty to the new charges on Friday, and he has denied all previous charges as well.

Manafort’s lawyers told Jackson on Friday that even if the contacts were improper, which they denied, she could limit the problem with steps short of jail, such as a no-contact order barring Manafort from contacting potential witnesses.

Jackson disagreed. “This isn’t middle school, I can’t take his cellphone,” she said, adding that she doubted she could draft an order comprehensive enough to ensure against any possible violations.

Eliza Fawcett is a special correspondent.

chris.megerian@latimes.com