Vice President-elect Kamala D. Harris resigned her Senate seat Monday at noon, stepping down four years after she was elected California’s junior senator and moving her one step closer to a historic tenure as the nation’s first female, Black and Asian American vice president.

Harris sent a formal letter notifying California Gov. Gavin Newsom, a longtime ally, of her intentions. Newsom has already said he will name California Secretary of State Alex Padilla to Harris’s seat.

Harris is scheduled to be sworn in alongside President-elect Joe Biden on Wednesday in an outdoor ceremony on the steps of the heavily guarded U.S. Capitol. Supreme Court Justice Sonia Sotomayor, the first woman of color named to the nation’s highest court, will swear in Harris, according to an aide.

Harris will make use of two Bibles in the ceremony — one belonging to her longtime hero, the late Supreme Court justice Thurgood Marshall, and the other belonging to Regina Shelton, a family friend who served as a second mother to Harris during her childhood.

Harris leaves behind a Senate that will be divided 50-50 between the parties, leaving the new administration with a daunting challenge in winning over enough Republican senators to enact its priorities, starting with coronavirus relief.

Harris spent much of her time in the Senate opposing President Trump’s legislation and appointees.

She made a name for herself interrogating Trump nominees and officials including Jeff Sessions, Brett M. Kavanaugh and William P. Barr. She sponsored a variety of bills to address racial inequities in the criminal justice system, health care and education, and advocated for rent relief and tax credits for the middle class.

Harris published an op-ed in the San Francisco Chronicle on Monday looking ahead to her new role as president of the Senate, part of the vice president’s duties. That role will assume greater importance in the evenly divided chamber, because Harris will cast the deciding vote if there are ties.

“Since our nation’s founding, only 268 tie-breaking votes have been cast by a Vice President. I intend to work tirelessly as your Vice President, including, if necessary, fulfilling this Constitutional duty,” Harris wrote. “At the same time, it is my hope that rather than come to the point of a tie, the Senate will instead find common ground and do the work of the American people.”

Harris, who chose to resign on Martin Luther King Jr. Day, is one of three Black senators. She is one of just two Black women ever to serve in the Senate, and many activists urged Newsom to choose a Black woman replace her.

In her op-ed, Harris recalled that it was just a year before she interned in the Senate, as a Howard University student in 1984, that Martin Luther King Jr. Day became a holiday.

“There was a heated debate and a fair amount of grandstanding. In the end, the Democratic-led House passed the bill, the Republican-controlled Senate did the same, and the Republican president signed it into law,” she wrote.

“Change is possible. For that, I am grateful and ready to get to work.”

Padilla, Newsom’s choice to replace Harris, will become the first Latino senator from California, a state with a population that is about 40 percent Latino. The state’s attorney general, Xavier Becerra, has been nominated by Biden to direct the Department of Health and Human Services.

Padilla will be up for election in 2022, while California’s senior senator, Dianne Feinstein, 87, will be up for reelection in 2024.