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WASHINGTON — Supreme Court nominee Brett Kavanaugh declined to answer several questions about the potential limits of presidential power over more than 12 hours of testimony at his confirmation hearing Wednesday, including his views on whether a president could be subpoenaed, fire a prosecutor investigating his actions or legally pardon himself.

Kavanaugh will face a second round of questions Thursday, with each senator allotted 20 minutes each.

In an exchange with Senate Judiciary Committee Chairman Chuck Grassley, R-Iowa, Kavanaugh said that “no one is above the law in our constitutional system.” He said that the best qualities of a judge are having independence — not being swayed by political or public pressure — along with respect for precedent and having collegiality and civility.

Sen. Dianne Feinstein, D-Calif., the committee's ranking member, pressed Kavanaugh about his views on whether a sitting president can be required to respond to a subpoena. Kavanaugh declined to answer the question because it was a "hypothetical" scenario.

"I can't give you an answer on that," said Kavanaugh, who worked earlier in his career for independent counsel Ken Starr during his investigation of President Bill Clinton.

Kavanaugh was also asked by Feinstein about his comments two decades ago that United States v. Nixon, which led to the release of the president's Oval Office tapes, might have been "wrongly decided," and that "if the president were the sole subject of a criminal investigation, I would say no one should be investigating that."

Kavanaugh did not directly address the merits of the decision, but said he had often praised it as "one of the four greatest moments in Supreme Court history" because the court stood up for judicial independence and against political pressure in a moment of national crisis.

Asked by Sen. Patrick Leahy, D-Vt., whether President Trump has a right to pardon himself, Kavanaugh said that he couldn't respond because he hadn't explored the topic.

"The question of self-pardons is something I've never analyzed. It's a question I have not written about... It's a hypothetical question that I can't begin to answer in this context," Kavanaugh said.

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Later on, Sen. Amy Klobuchar, D-Minn., asked Kavanaugh what kind of "dastardly" act by a president would constitute an impeachable offense.

"That is really a question for the House and the Senate," Kavanaugh said.

Sen. Chris Coons, D-Del., asked Kavanaugh about whether he stands by remarks from 1998 in which he said that presidents can fire prosecutors at will.

"That's a question of precedent," Kavanaugh said. "I think that question is governed by precedent that you'd have to consider." Pressed by Coons on whether he still believed a president can fire at will a prosecutor who is criminally investigating him, Kavanaugh demurred: "I think all I can say, senator, is that was my view in 1998."

Sen. Richard Blumenthal, D-Conn., continued to press Kavanaugh about possible judicial issues involving the president, asking if the nominee could commit to recusing himself if an issue involving Trump's civil or criminal liability were to come before the Supreme Court.

Kavanaugh responded that one key principle of independence of the judiciary was "not to make commitments on particular cases."

"I am troubled and disturbed," Blumenthal responded.

Toward the end of the hearing, Sen. Kamala Harris, D-Calif., asked if Kavanaugh had had a conversation about special counsel Robert Mueller or the Russia investigation he's overseeing with anyone who works at the law firm Kasowitz, Benson and Torres, founded by President Trump's personal lawyer Marc Kasowitz.

"I'm not remembering," Kavanaugh initially said. "I don't know everyone who works at that law firm."

Kavanaugh said he was sure he had spoken to fellow judges about the probe.

Democrats pressed the nominee on other front as well, including his views on reproductive rights and assault weapons and his experience in the George W. Bush White House. Leahy also asked Kavanaugh if former GOP Senate staffer Manny Miranda had provided him with specific information about what Democratic senators were planning surrounding Bush’s judicial nominees after he improperly accessed their computers in the mid-2000s, adding that there was evidence that Miranda provided Kavanaugh with material that was taken from Leahy, contradicting his prior testimony.

Kavanaugh responded that he had not known at the time that he was dealing with stolen property, and that his testimony had been accurate.

Sen. Sheldon Whitehouse, D-R.I., asked Kavanaugh to repeat what the nominee had told him recently about not being able to give any assurance that he would uphold a statute requiring insurance companies to protect people with pre-existing conditions. Whitehouse grew impatient with Kavanaugh, who initially tried to give a more comprehensive answer when the senator wanted a simple "yes" or "no."

"I can't give assurances on a specific hypothetical," Kavanaugh said.

Trump said Wednesday he was "happy with the Kavanaugh hearings."

"I watched today for a little while. I saw some incredible answers to very complex questions," the president told reporters at a White House event.

Kavanaugh faced opposition of a different sort beyond the dais: From the earliest moments of his morning comments, he was repeatedly interrupted by protesters, who were escorted out of the room. Grassley said as the session began that 70 people had been arrested during Tuesday's chaotic first day of hearings, with Capitol Police revealing as testimony ended Wednesday that another 73 people had been arrested.

The 53-year-old federal appeals court judge delivered his opening statement Tuesday in a Senate Judiciary Committee hearing that lasted nearly eight hours. The hearings are expected to continue through at least Friday.

Republicans are aiming to confirm Kavanaugh by the end of the month, before the high court’s next term begins in October. It appears almost certain that he will be confirmed, especially if Republicans stick together.

Former Sen. Jon Kyl, R-Ariz., Kavanaugh’s confirmation “sherpa” on Capitol Hill, will meanwhile be returning to the Senate after Arizona’s governor announced Tuesday that Kyl would fill the seat of Sen. John McCain, R-Ariz., who died Aug. 25 from brain cancer.