California Democratic Sen. Barbara Boxer, a tenacious liberal whose election to the Senate in 1992 heralded a new era for women at the upper reaches of political power, announced Thursday she will not seek re-election to a new term next year.

Boxer's retirement sets off a free-for-all among a new generation of California Democrats, who have been ascendant in the state for years with few offices to aspire to while Boxer and Sen. Dianne Feinstein have held a lock on the state's U.S. Senate seats.

A staunch supporter of abortion rights, gun control and environmental protections, Boxer has said she is most proud of the vote that she cast against the war in Iraq.

The 74-year-old Boxer made the announcement in an unusual video in which she answered questions posed by her grandson, Zach Rodham. "I am never going to retire. The work is too important. But I will not be running for the Senate in 2016," Boxer said.

In the video, Boxer's grandson is a surrogate reporter posing questions to her. Rodham is the son of Nicole Boxer and Tony Rodham, Hillary Rodham Clinton's youngest brother.

"I want to help our Democratic candidate for president make history," Boxer tells her grandson, a clear reference to a possible bid by Clinton.

She closed with a poem. "So although I won't be working in my Senate space and I won't be running in that next tough race, as long as there are issues and challenges and strife, I will never retire, because that's the meaning of my life."

Boxer was first elected to the House in 1982 and to the Senate one decade later. It was an election that marked a watershed year for women in politics, with four winning U.S. Senate seats. Boxer prominently displays in her office a photograph of her and six other female members of the House marching up the steps leading to the Senate, where they demanded that senators hold hearings on Anita Hill's allegations of sexual harassment against Supreme Court Justice Clarence Thomas before holding his confirmation vote.

Boxer's departure is a generational change as well. Boxer's fellow California senator, Feinstein, is 81, and House Democratic leader Nancy Pelosi is 74.

"I always knew I had a partner in Barbara," Feinstein said. "She is never one to shy away from any challenge, and I can't thank her enough for being such a resilient collaborator."

The news surprised Pelosi, who said at a Capitol Hill news conference she was unaware of Boxer's decision. Pelosi said the senator called earlier but that she missed the call.

"I thought she wanted to have dinner," Pelosi said. She described Boxer, who stands 4 feet, 11 inches tall, as "small in size but a giant in terms of contributions to her country."

White House spokesman Josh Earnest said President Barack Obama called Boxer to congratulate her on her retirement and her service.

Boxer had a way of riling conservatives. She can be abrupt with those who question or disagree with her, and she cemented her reputation as a firebrand with testy exchanges with witnesses at committee hearings over the years.

In 2009, she requested that a brigadier general in the Army Corps of Engineers call her senator instead of ma'am. The confrontation served as fundraising fodder for her election opponents the following year, but she still won handily.

And during the height of the war in Iraq, she challenged Secretary of State Condoleezza Rice's integrity by telling her that she believed her "loyalty to the mission you were given, to sell this war, overwhelmed your respect for the truth."

In her campaign ads, Boxer would constantly hammer home her feistiness and play on her last name by describing herself as a fighter.

Boxer would have been a prohibitive favorite to win if she had sought re-election in strongly Democratic California. Republicans have found it exceedingly difficult to find a candidate who can compete statewide.

Even before she announced her retirement, there was a great deal of speculation about possible Democratic candidates to succeed her. Among them: Lt. Gov. Gavin Newsom, a former San Francisco mayor; state Attorney General Kamala Harris; former Los Angeles Mayor Antonio Villaraigosa; and Tom Steyer, a retired San Francisco hedge fund billionaire who sought to make climate change an issue in the midterm elections. While lauding Boxer in prepared statements, none of the potential candidates indicated he or she would attempt to succeed her.

Statewide elections in California are hugely expensive and could require Republicans to side with a candidate who would significantly fund his or her own campaign, such as Rep. Darrell Issa or business executive Carly Fiorina, who lost to Boxer in her last race and is weighing a run for president. Another possible candidate is Fresno Mayor Ashley Swearengin, who waged a competitive race for state controller last year.

Republicans view the retirement as positive for the 2016 elections in part because it could mean that Democrats will have to spend money to retain the seat, which they probably would not have done if Boxer were in the race.

Still, the latest voter registration numbers in California show that Republicans will have an extremely difficult time, particularly during a presidential election when there's larger Democratic turnout. The latest voter registration statistics show that only about 28 percent of the state's voters are registered as Republicans.

"A California Republican starts every statewide race 15 points behind and is competing against arguably the most effective state political party in the country," said Republican strategist Aaron McLear, who also described the state as "nearly impossible for Republicans to win statewide."

Boxer narrowly won her first Senate race after a late revelation that her Republican opponent had attended a strip club. She won her three subsequent Senate races by double-digit margins.

Her job performance ratings over the years have consistently been more positive than negative, though they tend to lag behind ratings for Feinstein, who is viewed as more of a centrist and someone relied on by business groups in the state to get something through Congress.

Political observers say Boxer's work to protect the environment is probably her most significant legacy. Boxer authored legislation that has designated more than 1 million acres of land in California as wilderness, a classification that is the highest level of protection and generally does not allow for motor vehicles, new roads and mining. She also led efforts to prevent oil drilling in the Arctic National Wildlife Refuge in Alaska.

However, she has failed to help pass meaningful legislation to curb global warming, a longtime goal that became even more distant when Republicans won control of the Senate and Boxer lost her prized role as chairman of the Senate Committee on Environment and Public Works.

"I think she would say she's been a soldier in an ongoing fight that has yet to conclude," said Jack Pitney, a political science professor at Claremont McKenna College in California.

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