Attorney General William Barr told the House Judiciary Committee that he won’t show up for a scheduled hearing Thursday about Special Counsel Robert Mueller’s Russia investigation.

Barr is “trying to blackmail the committee,” Judiciary Chairman Jerrold Nadler told reporters this evening, saying that the executive branch doesn’t get to dictate the format of the hearing. Nadler added that he may issue a subpoena for the attorney general to show up if he doesn’t relent.

Barr’s decision not to attend the hearing dramatically escalates tensions with the Democratic-controlled committee, which has already authorized a subpoena to the Justice Department to obtain an unredacted version of Mueller’s report as well as the underlying evidence. Nadler said the Justice Department is refusing to hand over the full report and the panel may issue a contempt citation.

The Justice Department objected to the format of the planned hearing, which would let the committee’s Democratic and Republican counsels grill Barr for as long as 30 minutes at a stretch after an initial five-minute exchanges with lawmakers.

“Unfortunately, even after the attorney general volunteered to testify, Chairman Nadler placed conditions on the House Judiciary Committee hearing that are unprecedented and unnecessary,” Kerri Kupec, a Justice Department spokeswoman, said in a statement. “Chairman Nadler’s insistence on having staff question the Attorney General, a Senate-confirmed Cabinet member, is inappropriate.”

Nadler said he planned to convene the hearing as scheduled and hoped that Barr would reconsider his decision.

The back-and-forth could set up a protracted legal battle. Courts have reaffirmed Congress’s constitutional authority to issue and enforce subpoenas, but efforts to punish an executive branch official for non-compliance with a criminal subpoena have faced obstacles. In this case, it’s unlikely that the Department of Justice would pursue anything against the attorney general.

The standoff comes following a contentious hearing today when Barr testified before the Republican-controlled Senate Judiciary Committee. The hearing included tense exchanges between Barr and some senators, and resulted in multiple Democrats calling for the attorney general to resign.

Barr deflected attacks by Democrats on his decision to oppose an urgent request by Mueller to publicly release summaries of the Russia investigation, and he repeatedly excused conduct by President Donald Trump that the special counsel said could constitute obstruction of justice.

Barr went a step further, saying there’s evidence that Trump was the victim of false accusations.

Trump has been dogged “by two years of allegations —- by allegations that have now been proven false,” he said. At various points during the hearing, Barr said Trump was “falsely accused” of colluding with Russians and being a Russian agent, and that the evidence shows the allegation is “without a basis.”

Mueller, however, didn’t report that Trump was falsely accused. Instead, the report said that “while the investigation identified numerous links between individuals with ties to the Russian government and individuals associated with the Trump campaign, the evidence was not sufficient to support criminal charges.”

The special counsel’s report also said that “the investigation did not always yield admissible information or testimony, or a complete picture of the activities undertaken by subjects of the investigation.” Mueller’s team noted that some individuals invoked their Fifth Amendment rights against self-incrimination, while others provided “false of incomplete” information.

DEFINITION OF ‘FLIPPING’

At another point in the hearing, Barr described for the committee what he believed Trump’s lawyers would offer as a defense about an episode detailed in Mueller’s report where Trump sought to stop his former personal lawyer, Michael Cohen, from “flipping” and cooperating with law enforcement. He adopted the president’s definition of “flipping” — being persuaded by prosecutors to lie.

Barr several times described what he thought Trump’s motives were in some of the episodes that Mueller investigated for possible obstruction. But Mueller never secured an interview with Trump, who agreed only to answer limited written questions from the special counsel on selected topics. “He never pushed it,” Barr said of Mueller.

The hearing also examined disputes between Barr and Mueller, particularly Barr’s summary characterization of Mueller’s main conclusions.

But Democrats, including Hawaii Sen. Mazie Hirono, challenged Barr’s explanation of his differences with Mueller. Democratic leader Chuck Schumer said on the Senate floor that the disclosure raises “damning questions about his impartiality and about his fitness.”

Mueller contacted Barr to express his displeasure after Barr issued his four-page letter in March characterizing the main findings of Mueller’s investigation.

“The summary letter the department sent to Congress and released to the public late in the afternoon of March 24 did not fully capture the context, nature, and substance of this office’s work and conclusions,” Mueller wrote.

Mueller wrote that Barr’s letter created “public confusion” about important parts of the results of the special counsel’s 22-month probe. “This threatens to undermine a central purpose for which the Department appointed the special counsel: to assure full public confidence in the outcome of the investigations,” Mueller wrote in the letter reported Tuesday evening by the Washington Post.

While the Justice Department portrayed it as a friendly difference of opinion, Representative Adam Schiff, the Democratic chairman of the House Intelligence Committee said on “CBS This Morning” that Barr should resign because he “deliberately” misled Congress when he testified he didn’t know whether Mueller agreed with his summary of the findings.

Republican Sen. Lindsey Graham, the Judiciary panel’s chairman, opened the hearings by saying he was satisfied with Mueller’s report and said “for me, it is over.”

But Sen. Dianne Feinstein, the committee’s top Democrat, said that Mueller’s report contained “substantial evidence of misconduct” and that the committee needed “to hear directly from the special counsel.” Barr repeated his past statement that he’d have no objection to Mueller appearing before Congress.

Justice Department spokeswoman Kerri Kupec said in a statement Tuesday evening that Barr called Mueller after receiving the special counsel’s letter.

“In a cordial and professional conversation, the special counsel emphasized that nothing in the attorney general’s March 24 letter was inaccurate or misleading,” Kupec said in the statement. “But, he expressed frustration over the lack of context and the resulting media coverage regarding the special counsel’s obstruction analysis.”

Barr said in his letter, and in a news conference shortly before the report was released, that Mueller had closed his inquiry without deciding whether President Donald Trump had obstructed justice. Barr said that meant he needed to make the decision. He said that he, along with Deputy Attorney General Rod Rosenstein, concluded that there wasn’t sufficient evidence for criminal charges.

Barr’s characterization of Mueller’s findings stood uncontested until a redacted version of Mueller’s report was released on April 18.

In fact, Mueller said he didn’t make a “traditional” prosecution judgment on obstruction, mainly because he decided to abide by a Justice Department policy that says a sitting president cannot be indicted.

Yet he cited at least 10 examples of efforts to interfere in the investigation and pointedly added, “If we had confidence after a thorough investigation of the facts that the president clearly did not commit obstruction of justice, we would so state. Based on the facts and the applicable legal standards, however, we are unable to reach that judgment.”

Defending Barr’s call on obstruction of justice, Graham said Mueller told the attorney general “‘Mr. Barr, you decide’ — and Barr did.” Mueller never made such a request.

Sen. Amy Klobuchar, one of three Democratic presidential candidates on the Judiciary panel, cited a litany of instances in Mueller’s report from which Trump signaled those around him should stay on message, indicating he’d have lawyer Michael Cohen’s back or calling former campaign chairman Paul Manafort “a brave man” for refusing to break under pressure from prosecutors.

“You look at the totality of the evidence and the pattern here” of obstruction, she said.

Barr replied that a prosecutor would have to show that Trump had “corrupt intent” and that his statement would have a “sufficiently probable effect.” He said there’s “ample evidence” backing Trump’s version that he wanted to prevent people from “succumbing to pressure” and lying.

Graham and other Republicans on the committee renewed their call for an investigation into what he and other Republicans portray as anti-Trump sentiment that they say tainted the early stages of the Russia investigation and the 2016 investigation into Democrat Hillary Clinton’s use of a private email server. Barr affirmed that he’s looking into such issues, including what he’s previously called “spying” on Trump’s campaign. He said FBI Director Christopher Wray also was exploring that question.