For California Sens. Dianne Feinstein and Kamala Harris, there’s more at stake in this week’s Judiciary Committee hearings for Supreme Court nominee Brett Kavanaugh than his expected confirmation.

When the first of four scheduled days of hearings begins Tuesday, Kavanaugh and the future of the high court will be the focus. Feinstein, Harris and the other eight Democrats on the committee will be pushing hard to turn any wavering Republican senators — and public opinion — against the 53-year-old appeals court judge, whom President Trump nominated in July to replace retired Justice Anthony Kennedy.

In the end, a party-line vote to advance Kavanaugh to the full Senate with a favorable recommendation is the most likely outcome. So Feinstein, the panel’s ranking Democrat, and Harris, its most junior, will be looking for other victories.

For Feinstein, who faces a re-election challenge on the left from state Sen. Kevin de León, D-Los Angeles, in November, “it’s in her interest to come out strong,” said Sam Erman, an associate professor at the University of Southern California’s Gould School of Law.

That means showing progressives she shares their worries about both Kavanaugh and Trump. Even though she’s leading de León in the polls by a healthy margin, Feinstein has been losing progressive support since she voiced her hope last year that Trump could become “a good president.” In July, the state Democratic Party’s executive committee endorsed de León, a stunning if largely symbolic setback for the 25-year Senate veteran.

Harris, though, is already a favorite of Democratic progressives and could use the high-visibility confirmation hearing to help cement her support, including for a possible 2020 presidential run. The former San Francisco prosecutor also has a reputation as an aggressive questioner who hasn’t been afraid to anger Republicans in the past.

“She can carve out some space for herself in Democratic politics and score some points for her political future,” said Erman, who clerked for Kennedy and former Supreme Court Justice John Paul Stevens.

The California senators have made no secret of their dismay at the prospect of Kavanaugh becoming a likely fifth strongly conservative voice on the nine-member court. In July, Harris waited less than a half hour after Trump announced Kavanaugh’s nomination to come out against him.

“The Supreme Court has a profound impact on the rights — and lives — of all Americans,” she said in a statement. Kavanaugh “represents a direct and fundamental threat to (the) promise of equality, and so I will oppose his nomination to the Supreme Court.”

Feinstein has promised to lead the opposition to Kavanaugh. She voted against his 2006 nomination to the Washington, D.C., appeals court and refused an invitation to go to the White House to hear Trump name him to the court.

“President Trump has been crystal clear that he would put ‘pro-gun’ and ‘pro-life’ justices on the court and that Roe v. Wade would be overturned ‘automatically,’” she said after the nomination. Kavanaugh “appears to meet all of President Trump’s promises for how his candidate will rule on specific issues.”

But opposing Kavanaugh’s nomination is very different from stopping it, especially when Republicans hold a 50-49 Senate majority and the Democrats have a handful of vulnerable senators running for re-election in Trump-friendly states.

“When the president and the Senate are controlled by the same party, there may be a lot of drama and theater during a confirmation hearing, but the president generally gets his way,” said Erwin Chemerinsky, dean of the law school at UC Berkeley.

That doesn’t mean Democrats need to throw up their hands and surrender.

While Tuesday’s session is expected to be a staid, relatively short session to give Kavanaugh and the 21 Judiciary Committee members an opportunity to read their prepared statements, on Wednesday and Thursday each committee member will have up to 50 minutes to question the nominee on a virtually unlimited range of topics.

There’s plenty that still needs to be learned, Feinstein said.

“We — the Senate — and the American public must know where Judge Kavanaugh stands on the important issues before confirming him to a lifetime appointment,” she said.

On Friday, various witnesses will talk about Kavanaugh and the issues surrounding his nomination.

“Democrats can ask questions to trip (Kavanaugh) up, but he’s too smart for that ... and is not going to say anything to jeopardize his confirmation,” Chemerinsky said. “But they can also use their questions as a way to express views ... about what it will mean to switch from Kennedy to Kavanaugh.”

During his 30 years on the high court, the Sacramento-born Kennedy was a swing vote on a wide ranges of cases, including protection of abortion rights and legalization of same-sex marriage. Democrats worry that Kavanaugh would be a reliably conservative vote on these and other issues.

Speaking at a Democratic Unity Breakfast in Oakland in July, Feinstein said that while this will be the 10th Supreme Court nomination since she was first elected in 1992, Kavanaugh’s is “different from all of them ... because this man will be the deciding vote on most things we hold most dear.”

For Democrats, Kavanaugh threatens accomplishments they’ve spent years building.

Kavanaugh “is well outside the mainstream and threatens hard-won rights and protections for all Americans,” including abortion rights, health care, civil rights and worker protections,” Harris said in a statement released after she met with the nominee last month.

While Kavanaugh has been a federal judge for more than a decade, expect Democrats to concentrate on his years in politics, as an attorney working under independent counsel Kenneth Starr in the long-running Whitewater investigation that led to the impeachment of President Bill Clinton and later as White House staff secretary to President George W. Bush.

Kavanaugh’s actions and writings during those years could be a much better target for Democrats than the rulings he’s made as a judge, because he can always refuse to discuss issues that may come before him on the Supreme Court.

“It’s easier for Democrats to say that they’re not asking how he would vote, but what he meant in the speeches he’s made and the law review articles he’s written,” said Chemerinsky, the UC law dean. “It’s hard to argue that you can’t discuss what you’ve already made public.”

Democrats are especially concerned about a 2009 law review article in which Kavanaugh argued that Congress should protect a sitting president from civil suits, criminal investigations and prosecution while in office, so that the chief executive can “focus on his never-ending tasks with as few distractions as possible.”

With Trump, his staff and his presidential campaign already under investigation by Special Counsel Robert Mueller, Democrats worry about how Kavanaugh would rule if a case from that investigation came before the court.

“Democrats will call on him to recuse himself from any of those cases, which he wouldn’t, and it’s not appropriate,” said Erman of USC. “But they want to make him look partisan and political rather than judicial and impartial.”

The confirmation hearing may be little more than Kabuki theater, a stylized exercise where the outcome is already determined. But Feinstein, Harris and the other Democrats will play it out, making their points and painting a very different picture of Kavanaugh from the one Trump and the Republicans want to display.

It’s a national stage for both Feinstein and Harris, and the way they handle it could have political effects that last far beyond this week.

John Wildermuth is a San Francisco Chronicle staff writer. Email: jwildermuth@sfchronicle.com Twitter: @jfwildermuth