Vice President Kamala Harris will swear in Democratic strategist Laphonza Butler, the late-Sen. Dianne Feinstein’s interim replacement, at 3 p.m. ET Tuesday at the Capitol in Washington, D.C.

Butler was previously an adviser to both Hillary Clinton and Harris’ presidential campaigns in 2016 and 2020, respectively.

California Gov. Gavin Newsom tapped Butler, the president of EMILY's List — a Democratic political action committee (PAC) dedicated to electing pro-abortion Democratic women to office — for the vacant interim Senate seat late Sunday evening, just two days after Feinstein’s death.

Butler will be the only Black woman serving in the U.S. Senate and the first openly LGBTQ+ lawmaker to represent the Golden State in the upper chamber.

NEWSOM NAMES LAPHONZA BUTLER, FORMER KAMALA HARRIS ADVISER, TO FILL FEINSTEIN'S VACANT SENATE SEAT

Laphonza Butler in front of American flags

EMILY's List President Laphonza Butler addresses a Biden-Harris campaign rally on the first anniversary of the Supreme Court's Dobbs v. Jackson decision at the Mayflower Hotel in Washington, D.C., on June 23, 2023. (Chip Somodevilla/Getty Images)

Newsom, facing pressure to appoint someone quickly to keep the Senate’s Democratic majority, previously vowed to select a Black woman. He faced criticism after appointing then-Secretary of State Alex Padilla to replace then-Sen. Kamala Harris’ position before she assumed the vice presidency. There have been no Black women in the Senate since Harris left, Newsom noted.

Butler will finish out the remainder of Feinstein's term in Washington, D.C., ahead of the 2024 election. In a statement, the governor described Butler as an "advocate for women and girls, a second-generation fighter for working people, and a trusted adviser to Vice President Harris."

LONGTIME SEN. DIANNE FEINSTEIN PASSES AT AGE 90

Gavin Newsom and Laphonza Butler

California Gov. Gavin Newsom on Sunday announced that Laphonza Butler would replace Dianne Feinstein in the Senate.  (Tayfun Coskun/Anadolu Agency via Getty Images)

According to polls conducted by UC Berkeley and the Los Angeles Times last month, Rep. Adam Schiff is the leading candidate in the primary for Feinstein's seat with 20%, followed by Rep. Katie Porter with 17% and Rep. Barbara Lee and James Bradley trailing behind at 7%. The poll featured 6,030 California voters.

It's unclear if Butler will run to take on the seat full-time. In her first interview since Newsom's appointment, she told the Los Angeles Times, "I have no idea." 

"I genuinely don’t know," Butler told the outlet. "I want to be focused on honoring the legacy of Sen. Feinstein. I want to devote my time and energy to serving the people of California. And I want to carry her baton with the honor that it deserves, and so I genuinely have no idea."

GOP LAWMAKER ISSA DEMANDS ANSWERS FROM NEWSOM, SENATE LEADERS ON LAPHONZA BUTLER'S MARYLAND RESIDENCY

Senator Dianne Feinstein obituary photo

Sen. Dianne Feinstein died at the age of 90. (Fox News)

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Since the announcement of Butler's appointment, some GOP lawmakers have raised concerns about her residency status. 

Butler's home address is listed in Silver Spring, Maryland, and Rep. Darrell Issa, D-Calif., questioned the constitutionality of her ability to take office while residing in a different state than the one she will represent in a letter sent to Newsom and other lawmakers on Monday.

Newsom's office told Fox News Digital that Butler moved to the suburbs near Washington, D.C., when she became EMILY's List president in 2021, and that she has a house in California. The governor's office added that Butler will re-register to vote in California before she is sworn in.

"The quid pro quo of agreeing to pay your California taxes in return for becoming a senator is not an acceptable bargain," Issa said. "That's a privilege the rest of us don't get."

Fox News' Landon Mion and The Associated Press contributed to this report.