WASHINGTON — They are in lockstep in their demand for witness testimony, but nearly everything else Sens. Dianne Feinstein and Kamala Harris have said about President Trump’s impeachment trial has been different in both tone and substance.

In that sense, the California Democrats reflect their party’s conflicting approaches to the trial. Feinstein has publicly implored colleagues to embrace their role as impartial jurors, while Harris has laced into Trump like a prosecutor.

Their split speaks to the balancing act Democratic senators face in the trial that begins in earnest Tuesday: How can they help build the case against Trump to benefit their party politically, while fulfilling their duty as jurors?

The California senators’ different strategies were on display on the Senate floor in the days leading up to the House’s delivery of the two impeachment articles against Trump.

Harris used a Jan. 13 floor speech, her first significant address since ending her presidential campaign in December, to warn that America must not have two systems of justice, including one “in which powerful people like Donald Trump escape accountability altogether.”

“As the United States Senate, we must say that it’s unacceptable for a president to shake down a vulnerable foreign nation for personal or political benefit,” said Harris, the former San Francisco district attorney and California attorney general.

She even evoked the infamous “Access Hollywood” tape, 2005 footage that came to light during the 2016 presidential campaign, in which Trump bragged that he could freely grab women’s genitals because he was a celebrity.

Harris told The Chronicle afterward that she cited the tape to show Trump has “a level of arrogance that is consistent with his belief that the rules don't apply to him.”

Feinstein, meanwhile, has spoken little about Trump’s conduct in recent months. Instead, she has focused almost entirely on Democrats’ demand that current and former White House aides blocked by Trump from appearing before the House impeachment inquiry be allowed to testify before the Senate.

The 27-year veteran of the Senate and the Democrats’ highest-ranking member on the Judiciary Committee has urged her colleagues to adopt a somber, dutiful approach.

As Trump’s trial opened Thursday, Feinstein was part of a bipartisan group of four senators who escorted Chief Justice John Roberts into the chamber. Roberts will preside over the trial and swore in senators, who pledged to “do impartial justice according to the Constitution and laws.”

Feinstein is one of 16 current senators who heard the 1999 case against President Bill Clinton, who was acquitted of perjury and obstructing Congress in connection with his affair with a White House intern.

“The Clinton impeachment was incredibly sobering, and I expect the same for this trial,” Feinstein said in a statement. “I’ve said repeatedly that I’m prepared to listen to the evidence and decide on the articles of impeachment based on the merits.”

She has largely avoided giving detailed interviews about Trump’s trial, and her public comments have been sparse.

The outcome of the trial is essentially a given: Senate Republicans, who hold 53 of the 100 seats, are expected to acquit Trump. A two-thirds vote would be needed for conviction.

Trump is accused of abusing the power of his office by withholding military aid to Ukraine while pressuring its leader to announce investigations that could damage former Vice President Joe Biden, a rival in the 2020 election. He is also accused of obstructing Congress’ investigation by blocking witnesses from testifying and withholding subpoenaed documents.

Trump’s Republican defenders have said he was justified in withholding aid because of concerns about Ukraine’s long-standing problems with corruption.

It’s unclear how the Senate trial will unfold. Although Feinstein and Harris are part of the jury, senators are expected to be able to ask questions of House prosecutors and Trump’s legal team after the two sides give their opening arguments.

They may also vote on whether to hear from witnesses who did not testify before the House inquiry, something that is also outside the realm of traditional jury duty. Democrats, including Feinstein and Harris, are especially eager to hear from former National Security Adviser John Bolton, who was in his job as the Ukraine affair unfolded and has said he would testify if he is subpoenaed.

David Greenberg, a professor of history and media studies at Rutgers University, said the senators’ demeanor during the trial could help shape public sentiment as Americans remain sharply polarized over impeachment.

He said Feinstein and Harris’ approaches speak both to their different places in their political careers and to generational differences in the increasingly fractured Senate.

Harris is 55 and relatively new to the national stage, having been elected to the Senate in 2016. Although her presidential campaign failed, Harris has been mentioned as a possible vice-presidential candidate this year and could make another White House run down the line.

At 86, Feinstein is the oldest member of the Senate and is fifth in seniority. She came up in an era when senators were inclined to share dinner or drinks after a tough vote, not attack each other by name on the floor, and she has a reputation for being able to work with colleagues on both sides of the aisle.

“I think they’re products of different historical moments, they’re products of different political situations,” Greenberg said. “There are a handful of senators who are trying to uphold the old norms of collegiality and at least occasional bipartisan cooperation.”

Feinstein agreed that Harris and she “bring different but complementary experiences — a former prosecutor and attorney general and a senator who sat on the last presidential impeachment trial.”

“I look forward to hearing (Harris’) take on the House managers’ case and the president’s defense of his actions,” Feinstein said.

Sam Lauter, a Democratic political consultant in San Francisco, said Democrats may benefit from having both an aggressive prosecutor and a longtime fixture from a more polite era at the forefront of the trial.

“Both approaches are necessary to be able to have people look at this trial” with an open mind, he said.

But when it comes to questioning, Lauter said, he expects Harris’ prosecutor pedigree could emerge as a key weapon for Democrats as they make the case to the ultimate audience: 2020 voters.

“The country is going to see what a star Kamala Harris is,” he said. “This is going to be must-watch TV.”

Dustin Gardiner is a San Francisco Chronicle staff writer. Email: dustin.gardiner@sfchronicle.com Twitter: @dustingardiner