SAN FRANCISCO (KCBS) – Ending months of speculation, U.S. Senator Barbara Boxer announced on Thursday via YouTube that she will not seek a fifth term in 2016.

The announcement has already touched off debate about who might run to succeed her. “That’s one of the reasons I am announcing this early, to give everyone a shot, everyone a chance,” Boxer said in a conference call. “And let’s see who it is.”

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Potential candidates include Lt. Governor Gavin Newsom and Attorney General Kamala Harris. Both issued statements following the announcement.

“For over three decades, Senator Barbara Boxer has served the people of California with an unwavering commitment to bettering the lives of her constituents and all Americans. Senator Boxer is a true progressive champion and a tireless advocate for California’s priorities. I know she will never stop fighting for what matters, and I wish her all the best,” said Harris.

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“With the courage of her convictions and the unflinching spirit of a true warrior-advocate, Senator Barbara Boxer has earned a seat in the pantheon of great California leaders. On issue after issue, she has given voice to the voiceless, spoken truth to power, shined a bright light on injustices previously ignored, and brought dignity and honor to a profession that too often loses sight of those qualities. A champion for women and children and a force of nature for preserving our natural environment, her public service leaves a proud and indelible legacy,” Newsom said. “Growing up in Marin County, I remember Senator Boxer as my tenacious representative on the Board of Supervisors and I knew at a young age what every American everywhere now knows to be an immutable truth – there’s no “quit” in Barbara Boxer. While she might leave the Senate, she will never retire from her leadership on the progressive causes she’s led for decades. I wish Senator Boxer and her family the very best.”

Newsom and Harris, both Democrats, would not comment about a possible run. Also seen as contenders on the Democratic side of the ledger are billionaire environmentalist Tom Steyer and former Los Angeles Mayor Antonio Villaraigosa.  Possible Republican contenders include Neel Kashkari and Fresno Mayor Ashley Swearingen.

Los Angeles Mayor Eric Garcetti, a Democrat, and Republican Congressman Darrell Issa have already said they will not run.

For her part, Senator Boxer said she will fight for a progressive Democratic candidate who shares her concern to win to replace her.

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