Updated

California Sen. Dianne Feinstein announced Monday that she’ll seek re-election in 2018, ending speculation that she’d retire amid a potential primary challenge from the Democratic Party’s progressive wing.

The 84-year-old Feinstein has, until this week, deflected questions about seeking a full fifth term, telling NBC’s “Meet the Press" on Sunday: “I’m in a position where I can be effective. And, hopefully, that means something to California."

Feinstein, the oldest U.S. senator, was first elected to the chamber in 1992, in a special election. She would be 91 if she was re-elected in November 2018 and served the full six-year term.

Feinstein was mayor of San Francisco in the late 1970s after the assassination of Mayor George Moscone and Councilman Harvey Milk.

Progressives are purportedly frustrated enough about her views on President Trump, DACA and single-payer health care to mount a challenge for her seat.

She upset them last month when the Trump administration announced the dismantling of DACA, or Deferred Action for Childhood Arrivals, the Obama-era executive order that protects young illegal immigrants from deportation.

Feinstein said she supports DACA, but acknowledged the administration’s argument that the order is on shaky legal ground.

Her analysis came several days after being criticized at a town hall meeting in San Francisco for expressing optimism about Trump becoming "a good president.” The remark resulted in so much Democratic backlash that she issued a clarification about being “under no illusion” about Trump.

California Democrats until recently appeared on a nearly endless wait to rise in political circles -- with Feinstein and fellow Democrat Barbara Boxer as the state’s long-standing U.S. senators and fellow party member Jerry Brown serving four straight terms as governor.

However, Boxer’s retirement allowed former state Attorney General Kamala Harris last year to win that Senate seat. And Brown leaves in January after his fourth, and final, term.

Feinstein also has continuously expressed reservations about the so-called single-payer health care plan championed by many progressives, including Vermont Independent Sen. Bernie Sanders, a 2016 Democratic presidential candidate and a potential 2020 challenger.

Fox News’ Chad Pergram and Joseph Weber and the Associated Press contributed to this report.