Senate Intelligence Committee Chairman Richard Burr Richard Mauze BurrRep. Mark Walker says he's been contacted about Liberty University vacancy Overnight Defense: Trump rejects major cut to military health care | Senate report says Trump campaign's Russia contacts posed 'grave' threat Senate report describes closer ties between 2016 Trump campaign, Russia MORE’s surprise decision to subpoena Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE has set off an internal fight among Senate Republicans, some of whom are now pressing the North Carolina Republican to back off the request.

These Republicans argue that Trump Jr., the president’s eldest son, has spent enough time testifying before Congress and that the delivery of special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s report means it is time to end the investigations of the last presidential election.

“There’s no need for another subpoena for @DonaldJTrumpJr It’s time to move on & focus on issues Americans care about,” Sen. Ted Cruz Rafael (Ted) Edward CruzCruz blocks amended resolution honoring Ginsburg over language about her dying wish Trump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP MORE (R-Texas) tweeted Thursday.

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He was one of several Republicans in the House and Senate who was critical of the decision to subpoena Trump Jr., which Burr made in consultation with his panel’s ranking member, Sen. Mark Warner Mark Robert WarnerDemocrats call for declassifying election threats after briefing by Trump officials It's time to upgrade benefits Intelligence chief says Congress will get some in-person election security briefings MORE (D-Va.).

President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE said Thursday that he was “very surprised” by the subpoena, especially after Burr announced earlier that his panel had found no evidence of collusion between the Trump campaign and Russia.

“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 surprised,” Trump told reporters at the White House.

“I was very surprised. I saw Richard Burr saying there was no collusion two or three weeks ago,” Trump added.

Because of Burr’s comments in February to CBS News saying the panel did not “have anything that would suggest there was collusion by the Trump campaign and Russia,” Trump and his advisers were caught off guard by the Trump Jr. news.

White House acting chief of staff Mick Mulvaney Mick MulvaneyOn The Money: House panel pulls Powell into partisan battles | New York considers hiking taxes on the rich | Treasury: Trump's payroll tax deferral won't hurt Social Security Blockchain trade group names Mick Mulvaney to board Mick Mulvaney to start hedge fund MORE told CBS News in an interview Wednesday that he thought it “bad form” that he did not get a heads-up before the subpoena was issued.

It’s not clear if Trump Jr. will comply with the subpoena, though if he doesn’t it will just further add to the tensions in Washington.

Two congressional sources told Reuters Thursday that Trump Jr. is unlikely to comply with the subpoena and could cite his Fifth Amendment constitutional right against self-incrimination. Sen. Richard Blumenthal (D-Conn.), a member of the Judiciary Committee and former U.S. attorney, argued that the president’s son could be jailed if he tries to invoke executive privilege to avoid testifying.

Some Republicans worry that Burr, who has said he will not run for another term in 2022, is giving Democrats more ammunition by calling Trump Jr. to testify a second time before the Intelligence Committee about Russia’s activities during the 2016 election.

Burr this week said he’s not pursuing a criminal investigation against Trump Jr. and defended his panel’s work during a Senate GOP lunch meeting on Thursday, explaining the repeated efforts his staff made to secure Trump Jr.’s testimony.

“I think he walked through more the series of how many efforts were made prior to this to get them to … set a time,” Sen. Roy Blunt Roy Dean BluntSocial media platforms put muscle into National Voter Registration Day Senate GOP faces pivotal moment on pick for Supreme Court This week: Supreme Court fight over Ginsburg's seat upends Congress's agenda MORE (R-Mo.), a member of the Intelligence Committee, told reporters Thursday afternoon.

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Asked if members of the panel had received a heads-up about the subpoena, Blunt said the committee had previously decided to give Burr and Warner “extended subpoena authority and they used it.”

Burr agreed to subpoena Trump Jr. as part of an agreement with Warner to bring back key witnesses who previously only testified to committee staff.

Warner praised Burr for not rushing the investigation to an end in the wake of the Mueller report, despite pressure from other Republicans.

“I’m very proud of the fact that we’re the only committee that’s kept bipartisan through this whole investigation. The chairman’s had pressure to shut this down for a long time, I’ve had pressure to reach a conclusion before we’re finished,” he said.

Warner repeatedly declined to comment on the subpoena Thursday morning at a Christian Science Monitor breakfast but noted the panel has reserved the right to call back witnesses to answer additional questions or address “inconsistencies.”

“I’m not going to comment on specific witnesses,” he told reporters when asked if he was confident Trump Jr. had told the truth to the committee. “I will say that we have seen literally hundreds and hundreds of witnesses and the committee has been very clear with every one that we reserve the right to bring witnesses back if we have additional questions or there’s inconsistencies.”

Sen. Marco Rubio Marco Antonio RubioOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Democrats step up hardball tactics as Supreme Court fight heats up Press: Notorious RBG vs Notorious GOP MORE (R-Fla.), another member of the panel, said that colleagues had misinterpreted the committee’s work by assuming that Trump Jr. was being targeted over possible improper conduct.

“I just think there’s a fundamental misunderstanding about what the committee is focused on,” Rubio said.

“If at any point in time anything came across our information gathering that potentially could be of a criminal justice nature, that was referred to the special prosecutor. We’re not prosecutors,” he said. “I think sometimes when people read this they think we’re the same thing as the special counsel. Our role is very different.”

Rubio said the committee is not looking to ensnare Trump Jr. but instead is focused on the broader policy question of investigating Russia’s efforts to influence the election and recommend safeguards.

“We’re conducting oversight over the performance of the intelligence community in 2016, the nature of what Russia did and continues to do, what the threat is moving forward and what changes we need to make in our policies and laws to address that,” he said.

Burr told The Hill Wednesday, before news of the subpoena emerged, that he’s not trying to duplicate special counsel Robert Mueller’s investigation.

“I’ve got reports to do, they don’t have anything to do with the Mueller report,” he said, explaining that Congress doesn’t have responsibility over criminal matters, which should be referred to the Justice Department.

Sen. John Cornyn John CornynThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight Senate GOP faces pivotal moment on pick for Supreme Court MORE (R-Texas), another Intelligence Committee member and a member of the Senate GOP leadership team, warned that bringing Trump Jr. before the committee could inject politics into what has been so far a bipartisan investigation.

“At some point this is not about finding facts. This smacks of politics, and I think we have an important job to do to try to keep the Intelligence Committee out of politics and just keep ourselves focused on our mission, which is oversight of the intelligence community,” he said.

But other members of the panel said it made sense to bring Trump Jr. in to bring closure to an investigation that has spanned almost two years.

“I think they just wanted to get some questions straightened out, some answers straightened out based on people who came later,” Blunt said, referring to witnesses who testified after Trump Jr.

Rubio said Burr doesn’t want to leave any questions left open before filing his report, which members of his panel expect to be finished by the end of August.

“When you write a report, and you’ve gone this far and you’ve done this much work, there’s no point in not leaving nothing unchecked,” Rubio said.

Morgan Chalfant contributed.