WASHINGTON — Just seconds into the Supreme Court confirmation hearing of Justice Brett M. Kavanaugh in 2018, Senator Charles E. Grassley, then the chairman of the Judiciary Committee, was interrupted by a sharp demand to be recognized from far down the Democratic side of the dais.
“We cannot move forward, Mr. Chairman, with this hearing,” Senator Kamala Harris of California, the most junior Democrat on the panel, insisted after Mr. Grassley tried repeatedly to silence her — first by ignoring her and then by declaring her out of order.
Today, she remains the lowest-ranking Democrat on the panel. But when the Judiciary Committee convenes on Monday to consider the nomination of Judge Amy Coney Barrett to the Supreme Court, Ms. Harris will take on an outsize role in the proceedings as the party’s vice-presidential nominee. Almost as many eyes will be on her as on Judge Barrett.
Her seat on the panel will provide Ms. Harris a prominent platform to frame the stakes of Judge Barrett’s nomination for voters and amplify the message that Joseph R. Biden Jr., the party standard-bearer, is pressing in the final weeks of the campaign. But it will also require her to strike a delicate balance — one that she has been forced to calibrate ever since she joined Mr. Biden on the Democratic ticket — between being on the attack and coming across as sincere and broadly appealing.
Colleagues say that Ms. Harris’s capable turn at the debate last week against Vice President Mike Pence made it clear that she will have done her homework and be unafraid to challenge Judge Barrett, arguing that she poses a grave threat to the Affordable Care Act and abortion rights. But no one expects Ms. Harris to take any kind of confrontational risk that could backfire and alienate voters, especially given Mr. Biden’s steady lead in the polls over President Trump.
“Kamala Harris has already shown herself to be well grounded and well prepared, but also able to ask pointed questions,” said Senator Chris Coons, Democrat of Delaware and a fellow member of the panel. “She will help make clear to the American people the enormous consequences of Judge Barrett being confirmed to the Supreme Court.”
Ms. Harris is not the only member of the committee in the middle of a contentious race. Four Republicans — Lindsey Graham of South Carolina, Thom Tillis of North Carolina, Joni Ernst of Iowa and John Cornyn of Texas — also face the voters in a matter of days. They hope to use the hearings to bolster Republican enthusiasm while avoiding any political missteps.
Mr. Graham, the committee chairman in an unexpectedly difficult fight back home, is in a particularly visible role. He will be under fire for proceeding with a hearing Democrats consider out of bounds given its proximity to the election.
In the debate, Ms. Harris sought to drive home the point that Republicans were rushing the nomination against historical precedent, noting that Abraham Lincoln in 1864 deferred his opportunity to fill a Supreme Court seat that came open only weeks before the election.
“Joe and I are very clear,” she said, “the American people are voting right now and it should be their decision about who will serve on this most important body for a lifetime.”
Ms. Harris had planned to attend the hearings in person unless health and safety considerations arose. But on Sunday, she announced that she would instead monitor the proceedings from her Senate office, reinforcing the Democratic argument that Republicans are acting irresponsibly in pushing forward with the hearings even as the coronavirus has infected members of the committee.
Still, Republicans expect Ms. Harris to be among the most outspoken against the nomination, given her prominent political role and their memory of her participation in Justice Kavanaugh’s hearing and other Senate confirmation battles.
After her selection by Mr. Biden, Mr. Trump accused her of being “extraordinarily nasty” to Justice Kavanaugh in her questioning. In the debate, Mr. Pence recalled that Ms. Harris had questioned another judicial nominee’s views because he belonged to the Knights of Columbus, an organization for Catholic men.
In a conference call with reporters this month, Mark Meadows, the White House chief of staff, suggested that Ms. Harris would be under pressure to take on Judge Barrett at the hearings.
“I don’t think we will see less of Kamala,” he said. “I think we will see more of Kamala as it relates to her interaction.”
Democrats say the criticism from Republicans reflects their concern about the abilities of Ms. Harris, a former prosecutor, when grilling witnesses.
“I think this is an opportunity for her, because she is just so great as a questioner and as a force for justice,” said Senator Richard Blumenthal of Connecticut, another Democrat on the panel.
In the Kavanaugh hearings, Ms. Harris quizzed the nominee on a variety of topics such as abortion rights and Mr. Trump’s comment about a white supremacist rally in Charlottesville, Va., in 2017 that there was “blame on both sides.”
“Do you, sir, believe there was blame on both sides?” she asked with the direct accusatory style of a prosecutor. Justice Kavanaugh refused to answer, saying judges needed to “stay out of commenting on current events.”
Probably her most noted line of inquiry, though, came up empty after a nearly eight-minute exchange with Justice Kavanaugh over whether he had discussed the special counsel investigation of Mr. Trump and Russia with any lawyers at a firm founded by a lawyer for the president.
“Be sure about your answer, sir,” Ms. Harris warned the nominee in a tone that intimated she knew the answer and it was not good for Justice Kavanaugh. He responded that he was unsure, since Ms. Harris would not provide a name.
After some investigation, Justice Kavanaugh responded the next day that he had not discussed the inquiry with anyone at the firm. The issue died, and Republicans scoffed that Ms. Harris looked foolish.
“I hope the Democrats have learned from the antics of 2018 that they looked pretty bad and some of the most aggressive questioning came from Harris and some of the things that lacked any credibility whatsoever came from her,” said Mr. Grassley, Republican of Iowa, who remains on the committee but is no longer chairman.
Democrats on the panel said they anticipated that Ms. Harris would join them in trying to use the hearings to showcase policy divisions with Republicans over the health care law, emphasizing the possibility that Judge Barrett could join four other conservatives on the court in overturning it. They said they expected that Ms. Harris would consult with Mr. Biden, a longtime former chairman of the Judiciary Committee, about how to approach the hearing.
They also noted that she had her hands full running for vice president and would most likely have to dip in and out of the proceedings.
“She is,” Senator Mazie Hirono of Hawaii said, “a tad busy.”
Nicholas Fandos contributed reporting.