• Former House Speaker Nancy Pelosi said she will back Democratic Rep. Adam Schiff in the 2024 U.S. Senate race in California but only if Sen. Dianne Feinstein does not seek reelection.
• Feinstein, at 89, is the oldest sitting senator.
• The endorsement comes a week after Schiff, the former chairman of the House Intelligence Committee, launched his bid for the coveted seat.
• The race is already competitive, as Democratic Rep. Katie Porter announced Jan. 10 that she will run for the seat.

Former House Speaker Nancy Pelosi endorsed fellow California Democrat Rep. Adam Schiff on Thursday in the already competitive 2024 U.S. Senate race for the seat currently held by Dianne Feinstein.

But Pelosi said the endorsement applies only if Feinstein, who at 89 is the oldest sitting senator, decides not to seek reelection.

If Feinstein does run for another term, then "she has my whole-hearted support," said the 82-year-old Pelosi, who in November stepped down as the long-serving House Democratic leader after Republicans won the chamber majority in the November midterm elections.

A spokesman for Feinstein's office did not immediately respond to CNBC's request for comment on Pelosi's statement.

"If she decides not to run, I will be supporting House Intelligence Committee Chair Adam Schiff, who knows well the nexus between a strong Democracy and a strong economy," Pelosi said in a statement released by Schiff's Senate campaign Thursday morning.

"In his service in the House, he has focused on strengthening our Democracy with justice and on building an economy that works for all," Pelosi said.

Pelosi said the 62-year-old Schiff, who first ran for Congress in 2000, has dedicated his life to public service. "Every time I have asked Adam to take on the tough fight against extremist forces, he has responded with integrity, strength and success," she said.

The endorsement comes one week after Schiff, the former chairman of the House Intelligence Committee, launched his bid for Feinstein's coveted Senate seat. His announcement framed him as a fighter against Republicans and played up his one-time role as the top impeachment manager in the first Senate trial of former President Donald Trump. Pelosi had picked him for that role, which ended in Trump's acquittal by the GOP-led Senate.

"They aren't going to stop. We have to stop them. That's why I'm running for the U.S. Senate," Schiff said in a campaign-launch video.

Feinstein, meanwhile, has not yet said whether she will run again or retire at the end of her term. Her Senate campaign raised little money in the final months of last year, recent campaign filings show, a signal to some that she may not be preparing for another run.

Schiff was not the first Democrat to jump into the race for Feinstein's seat. Democratic Rep. Katie Porter announced Jan. 10 that she will run for Senate in California, snagging the endorsement of Sen. Elizabeth Warren, D-Mass.

Pelosi's announcement through Schiff's campaign began with effusive praise for Feinstein and her lengthy career in politics.

"Since her election to the Senate in 1992, Senator Feinstein has achieved a remarkable legislative record, always delivering for California and forcefully honoring her oath to protect and defend," Pelosi said. She referenced Feinstein's work on the 1994 assault weapons ban, as well as on the Violence Against Women Act and the Respect for Marriage Act, among other highlights.

"America is at a crossroads. We can continue to lift our communities, strengthen our economy and defend our Democracy — or let Republicans roll back our progress, threaten our freedoms and give tax breaks to the wealthy special interests," Pelosi's statement said. "In 2024, the fight for America's future is on the ballot."