California Attorney General Kamala Harris became the first high-profile Democrat to announce plans to enter the 2016 race to replace retiring Sen. Barbara Boxer in the U.S. Senate.

Harris, California's top prosecutor, made the announcement Tuesday on her website.

"I want to be a voice for Californians," she wrote, adding that fighting crime, fighting for consumers and fighting for equal rights are her top concerns. Her announcement also came with a big red "Donate" button underneath, and political analysts say a U.S. congressional seat run could cost at least $50 million to get through the June primary, and at least that amount to get through the fall campaign.

Gerston predicted that in all, complete with Political Action Committees, Super PACS and candidate fundraising, the total spent could be $1 billion for the first time in any state.

Her announcement came as no surprise to veteran political watchers. Analyst Larry Gerston predicted last week that her name would be on the short list of candidates. But he did add that she has an uphill struggle. Women of color, he said, "have yet to achieve parity with white males."

Harris, 50, a former two-term San Francisco district attorney, is a personal friend of President Barack Obama and attracted national attention when she helped negotiate a settlement with major mortgage lenders and secured extra funding for California. In 2013, Obama took a little heat for calling his pal the "best looking attorney general" during a fundraising event, which he later apologized for.

She has been widely viewed as an eventual candidate for governor or U.S. senator, a seat held by Boxer, 74, for more than two decades. Boxer's announcement last week that she will not seek a fifth term threw open the door for California Democrats seeking to climb the political ranks.

The disclosure of her plans through sources Monday afternoon came just a few hours after a potential rival, California Lt. Governor and former San Francisco Mayor Gavin Newsom, said he would not run for the open seat created by Boxer's retirement next year.

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, are also considered potential candidates for the seat. Democrats are well positioned to retain the seat in a state where the party controls every statewide office and both chambers in the Legislature.

As the state's chief law enforcement officer, Harris has focused her crime-fighting efforts on cross-border gangs that she said are increasingly engaged in high-tech crimes such as digital piracy and computer hacking to target businesses and financial institutions.

In 2010, Harris was elected California attorney general, becoming the first woman and the first minority to hold the office. She is the daughter of an Indian mother and black father. She was born in Oakland, graduated Howard University and the University of California, Hastings College of the Law. And before becoming San Francisco's DA, was a deputy district attorney in Alameda County.

Newsom's exit provided encouragement for others contemplating a run for the Senate, and his statement did nothing to dampen the idea he would run for governor in 2018 -- when the term of current Gov. Jerry Brown ends.

"I know that my head and my heart, my young family's future, and our unfinished work all remain firmly in the state of California -- not Washington, D.C. Therefore I will not seek election to the U.S. Senate in 2016," said Newsom, who has three young children.

Newsom launched a brief campaign for governor before dropping out in 2009. He is best known for ordering the San Francisco city clerk in 2004 to ignore state law at the time and issue marriage licenses to same-sex couples.

"They're longtime allies," said Gerston. "Given that, it makes sense that two big shots would divide and conquer."

NBC Bay Area's Cheryl Hurd contributed to this report.