By SHERYL GAY STOLBERG, New York Times–

Democrats who once saw health care and abortion as their best lines of attack against Judge Brett M. Kavanaugh, President Trump’s Supreme Court nominee, are recalibrating their approach to go after him for his view that a sitting president should not have to answer questions in a criminal case, much less face indictment.

Senator Chuck Schumer of New York, the Democratic leader, said in an interview on Wednesday that Judge Kavanaugh’s belief in broad presidential authority was “just off the deep end.”

For Democrats facing an uphill struggle to block Judge Kavanaugh’s confirmation, his protective views of the presidency could prove to be a bright red ribbon. Rather than just playing it safe with a broad swath of voters worried about access to health care and abortion, Democrats now see an opportunity to excite their base by fanning fears that the highest court in the land could turn into a bulwark to protect the man appointing its members.

As the judge made the rounds of the Capitol — he paid courtesy calls on Senator John Cornyn of Texas, the No. 2 Republican, and Senator Lindsey Graham, Republican of South Carolina — Mr. Schumer and his Democratic colleagues were gaming out a line of questioning that, they hope, will create a perception that a Justice Kavanaugh would compromise the independence of the court.

Mr. Schumer said the questions could appeal even to more moderate voters.

a man standing in a room: Senator Chuck Schumer, the Democratic leader, with a staff member during a press conference about Judge Kavanaugh on Wednesday. In an interview, Mr. Schumer said questions of Judge Kavanaugh’s stance on presidential power could resonate with moderate voters.© Lawrence Jackson for The New York Times Senator Chuck Schumer, the Democratic leader, with a staff member during a press conference about Judge Kavanaugh on Wednesday. In an interview, Mr. Schumer said questions of Judge Kavanaugh’s stance on presidential power could resonate with moderate voters.

“This issue, I think, will affect a lot of people who are sort of O.K. with Trump but think there needs to be a check and balance,” Mr. Schumer said. “There are a lot of people in America who still say, ‘I voted for him, I guess he’s O.K.’ But when you ask them, ‘Does he need a check and balance?,’ they say, ‘Definitely.’”

In two law journal articles — one published in 1998 and another in 2009 — Judge Kavanaugh raised questions about whether a sitting president could be indicted, and suggested that presidents should be shielded from civil suits and criminal investigations. Both explore issues that are deeply relevant to Mr. Trump and the ongoing investigation into Russia’s interference in the 2016 election.

Even before Mr. Trump chose his nominee for the court, Democrats had decided that they would focus almost exclusively on abortion and health care, issues that “resonate very deeply in America,” Mr. Schumer said earlier this week. But their lines of attack have expanded.

Republicans are pushing back, accusing Democrats of distorting the judge’s words. (In a fact-checking article published Wednesday, The Washington Post gave Democrats “two Pinocchios” for some of their claims about Judge Kavanaugh, and concluded that there was “no smoking-gun evidence that he would vote to dismiss an indictment against Trump, should one ever be filed.”)

Mr. Cornyn said he asked Judge Kavanaugh about the law journal articles during their “courtesy visit” on Wednesday. He said the judge noted that he had proposed that Congress impose limits on investigations of sitting presidents.

“He said, ‘If you read the law review article, this basically makes clear that this is a decision for Congress to make, not the courts,’ and he was writing from his experience in the Clinton impeachment matter,” Mr. Cornyn said, referring to Judge Kavanaugh’s time on the staff of the independent counsel, Kenneth W. Starr.

He added: “It was a law review article. Lawyers think about these issues and come up with proposed ideas, but it doesn’t really bear on his fitness to be on the Supreme Court.”

Democrats are making the case that Judge Kavanaugh should pledge to recuse himself from any case involving Mr. Trump’s financial dealings or the Russia investigation.

“For me it’s a threshold qualifying question,” said Senator Richard Blumenthal, Democrat of Connecticut. “If he is unwilling to state that he will recuse himself, I think everyone should really reconsider whether they can support this nominee.”

Those arguments could energize Democratic voters before the midterm elections. Whether they will be enough to sway Senate Democrats from Republican states or moderate Republicans whose votes are critical to Judge Kavanaugh’s confirmation remains to be seen.

One key swing vote, Senator Susan Collins, Republican of Maine, spoke favorably of Judge Kavanaugh on Wednesday, noting that the articles reflected Judge Kavanaugh’s “contemplation of his role in the Clinton impeachment.”

“This was long before there was a Russia investigation and long before Donald Trump was president, so I think those who are trying to draw a link here are missing the timeline,” Ms. Collins said. “But nevertheless it’s an issue that I certainly will raise with him.”

Democrats hope that more issues will arise as senators comb through Judge Kavanaugh’s writings and opinions. The nominee’s paper trail is so long that Rod J. Rosenstein, the deputy attorney general, has asked federal prosecutors to help review the judge’s government documents to speed the confirmation process, according to a letter obtained by The New York Times on Wednesday.

The Democrats’ argument on presidential power may not sway Republican senators, but it will resonate with voters, said Geoff Garin, a Democratic pollster.

“Voters, including many independent voters and some Republican voters, care deeply about maintaining the Supreme Court as an independent check and balance on the power of the president,” Mr. Garin said. “Our polling in red states shows that voters would approve of their senator voting against confirmation if he or she believed that the nominee would weaken the court’s role as providing an independent check and balance.”

The articles grew not only out of Judge Kavanaugh’s experiences working for Mr. Starr, but also his service to former President George W. Bush. They are entering the public discourse just as Robert S. Mueller III, the special counsel, has suggested he may subpoena the president as part of his inquiry into whether the Trump campaign colluded with Russians to influence the 2016 election, and whether Mr. Trump obstructed justice.

“Whether the Constitution allows indictment of a sitting president is debatable,” Judge Kavanaugh wrote in the Georgetown Law Journal in 1998. He proposed that Congress adopt legislation specifying that the president “is not subject to indictment or information under the laws of the United States while he serves as president.”

In 2009, writing in the Minnesota Law Review, he argued that civil suits and criminal investigations are a burdensome distraction for a president: “Like civil suits, criminal investigations take the president’s focus away from his or her responsibilities to the people. And a president who is concerned about an ongoing criminal investigation is almost inevitably going to do a worse job as president.”

There is precedent for a Supreme Court nominee to be grilled on his view of executive powers relating to a special counsel investigation, said Nan Aron, the founder and president of Alliance for Justice, a liberal advocacy group. In 1987, Judge Robert H. Bork, a Supreme Court nominee of Ronald Reagan’s who ultimately did not get confirmed, was questioned extensively about his role in dismissing Archibald Cox, the special prosecutor who was investigating President Richard M. Nixon.

But Carrie Severino, chief counsel for Judicial Crisis Network, a conservative advocacy group, drew a different Nixon parallel, noting that of four justices appointed by Mr. Nixon, three — Warren E. Burger, Harry A. Blackmun and Lewis F. Powell Jr. — sat on U.S. v. Nixon, the case in which the Supreme Court ordered Nixon to comply with a subpoena — and joined the unanimous decision against the president.