Gavin Newsom takes himself out of Boxer race*

Lt. Gov. Gavin Newsom said today he won't be among the Democrats running for the U.S. Senate seat to be vacated in 2016 by Sen. Barbara Boxer. Newsom took to Facebook to make his intentions known.

“It's always better to be candid than coy," Newsom posted. "While I am humbled by the widespread encouragement of so many and hold in the highest esteem those who serve us in federal office, 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.

“In the months to come, I look forward to doing whatever I can to help elect California's next great Democratic Senator – one worthy of succeeding Barbara Boxer and serving this remarkable state of dreamers and doers in the United States Senate.”

Newsom's exit lends credence to the sense that leading Democrats in Northern California are falling in behind Attorney General Kamala Harris. But there's also billionaire climate change activist Tom Steyer and former mayor Antonio Villaraigosa to possibly contend with — though the Sacramento Bee story this morning did not deem Villaraigosa mentionable. Villaraigosa announced on Saturday that he is looking seriously at the race.

Politico sees the possibility of an arrangement between Newsom and Harris.

Both Harris and Newsom, who started their careers in Northern California, have been waiting for chance to run for higher office. But operatives close to the two have said they expected Harris and Newsom to form a pact so that they don’t have to run against each other. For instance, one would run for Boxer’s seat while the other would agree to wait until 2018, when the state’s governorship and potentially the other Senate seat could be open if longtime Sen. Dianne Feinstein also retires.

* Added: Mark Z. Barabak of the LA Times provided a nice set-up for this turn of events in his Friday analysis of the Boxer decision. He suggested that Newsom and Harris would have to work out some sort of peace since, as he noted, they share "along with relative youth, good looks and irrepressible ambition, the same geographic and donor base in the San Francisco Bay Area."

The two liberal Democrats even have the same set of political advisors, who guided them from local office, as San Francisco mayor and district attorney, respectively, to their statewide positions in Sacramento.

This has led to a widely held belief that the pair will sit down, in the manner of conquerors dividing their spoils, to figure out who seeks Boxer’s seat in 2016—a seeming shoo-in for any Democrat—and who will run to succeed Gov. Jerry Brown in 2018, or, possibly, pursue another open Senate seat should Dianne Feinstein retire when her term ends in three years.

Newsom, 47, and Harris, 50, have had a cordial but not especially warm relationship; their close quarters and parallel ascent up the political ladder have kept the two in steady competition, one eye cast warily on the other.

It makes perfect sense, though, for one to stand aside in the Senate race, lest each seek the office and, in a crowded field, thwart the efforts of both by splintering the Northern California vote.