Supreme Court hopeful Brett Kavanaugh declined to answer Wednesday whether a sitting president can be required to comply with a subpoena, a question Democrats were expected to revisit during this week's confirmation hearings.

“As a matter of the canons of judicial independence, I can’t give you an answer on that hypothetical question,” Kavanaugh told Sen. Dianne Feinstein, D-Calif., the top Democrat on the Senate Judiciary Committee.

Kavanaugh’s views on executive power, including whether a sitting president is required to respond to a subpoena, are expected to be a key part of his confirmation hearing, especially given the ongoing investigation into Russian meddling in the 2016 election. During Wednesday morning's questions, he cited previous answers from sitting Supreme Court justices who also declined to give their views on hypothetical cases.

“I follow the precedent of the nominees who have been here before,” he said.

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Kavanaugh was also asked specifically about the Supreme Court’s ruling in the 1974 case U.S. v. Nixon, which forced President Richard Nixon to turn over the Watergate tapes. President Trump’s Supreme Court nominee called the unanimous decision one of the four “greatest moments in Supreme Court history."

The court, he said, “stood up for a moment of judicial independence” during a national crisis. “No one is above the law,” Kavanaugh said of the president.

Kavanaugh has faced criticism from Senate Democrats for his views on executive power, in part because of a 2009 Minnesota Law Review article he wrote about investigations involving sitting presidents. Some have argued those writings indicate Kavanaugh does not believe a sitting president should be under investigation, but Kavanaugh told the Judiciary Committee he was proposing ideas for Congress to consider.

[Brett Kavanaugh: 'I am a pro-law judge']

“They were not my constitutional views,” he said.

Kavanaugh said that if a case raising the question of whether a sitting president can be under investigation comes before the court, he would “have a complete open mind.”

Feinstein asked Kavanaugh what changed his views on investigations occurring during a presidency, given his tenure working for independent counsel Ken Starr’s investigation involving President Bill Clinton.

“What changed was Sept. 11, that’s what changed,” he said. "After Sept. 11, I thought very deeply about the presidency and I thought very deeply about the independent counsel experience and I thought very deeply about how those things interacted.”