Senate Republicans fractured today over the news that the GOP-led Senate Intelligence Committee subpoenaed the president’s eldest son, Donald Trump Jr., for another round of testimony in its long-running Russia investigation.

Trump Jr.’s allies waged a Twitter campaign — backed by his own retweets — against the subpoena aimed at pressuring Intelligence Chairman Richard Burr to end his investigation. Burr appeared unmoved, declining to comment to reporters.

Republicans including Rand Paul of Kentucky, Ted Cruz of Texas and Thom Tillis — who faces a primary challenge in Burr’s North Carolina next year — opposed the subpoena on Twitter, with Tillis saying it’s “time to move on.” They aren’t members of the Intelligence Committee, which has been investigating Russian interference for more than two years under Burr’s leadership.

All the members of the Senate Intelligence panel have known about the subpoena since it was issued weeks ago, according to a person briefed on the committee’s process.

Senator Roy Blunt, a member of GOP leadership and the Intelligence committee, noted that Trump’s senior adviser and son-in-law Jared Kushner had previously returned to the committee for more questioning.

“Hopefully Don Jr. and his lawyers will believe it’s important — I think his brother-in-law came in in a similar situation to be sure that every question was clearly understood and clearly answered, and I think he should too,” the Missouri Republican said.

Blunt said he didn’t think any questions being asked would change the ultimate conclusion of the committee, and said the committee could be finished in August.

Burr has previously said he’s not running for re-election in 2022, which insulates him from retaliation. The president had previously lauded Burr for telling reporters he hadn’t found evidence of collusion between Trump and Russia in 2016.

Senator Richard Shelby of Alabama, a former chairman of the Intelligence Committee, also defended Burr, noting that people on the committee know far more than those who aren’t.

“We have confidence in our chairman,” he said. “I think the caucus will back the chairman.”

The president told reporters today that he was surprised by the subpoena of his son.

“Frankly, for my son, after being exonerated, to now get a subpoena to go again and speak again after close to 20 hours of telling everybody that would listen about a nothing meeting, yeah, I’m pretty surprised,” Trump said during a White House event.

The committee wants Trump Jr. to respond to testimony by the president’s former fixer, Michael Cohen, on the Trump Tower Moscow project, a person close to Trump Jr. said.

The proposed tower in Moscow was the brainchild of Cohen and Felix Sater, a former Trump associate who chased property deals for the future president. The pair pursued a potential tower in Moscow well into the 2016 presidential campaign — Cohen has said he regularly briefed members of the Trump family of their progress — but nothing came of it.

Trump Jr. told the Senate Judiciary Committee in September 2017 that he knew “very little” about Cohen and Sater’s attempt to build a Trump-branded tower in Russia’s capital.

His testimony sharply contrasts with what Cohen told the House Oversight Committee in February. Cohen, who this week began serving a three-year prison sentence for bank fraud and lying to Congress, said that he briefed Trump Jr. and his sister Ivanka about the project’s status about 10 times until Cohen, Sater and the Trump Organization abandoned their efforts in mid-2016 after reports began to surface of Russia’s interference in the presidential campaign.

Trump Jr. spent about 27 hours testifying to various congressional panels about Russia-related matters, said the person close to the president’s son. The person said that Trump Jr. may be willing to answer some written questions, but that no lawyer would agree to allow a client to participate in a public relations stunt.

Judiciary Chairman Lindsey Graham, a top Trump ally, said he didn’t want to second-guess Burr but sounded sympathetic to Trump Jr.’s reluctance to testify again.

“Just put yourself in Don Jr.’s place. In this environment would you go to round five or whatever it would be?” Graham of South Carolina said.

Democrats on the Intelligence Committee declined to comment on the subpoena itself.

But Senator Ron Wyden of Oregon, a senior Democrat, noted discrepancies in Trump Jr.’s publicly released testimony and that of Cohen on the level of their coordination on the Trump Tower Moscow project during the campaign.

“I, based on statements on the public record, have substantial questions about whether Donald Trump Jr. has been truthful,” Wyden said.

Wyden has said repeatedly that the Senate probe shouldn’t end until it has fully investigated “follow the money” issues as part of their counterintelligence probe, saying that’s how Russia tries to compromise people.