Last week’s Supreme Court decision on marriage equality was a huge victory for Mayor Gavin Newsom. Beyond vindicating his move in February 2004, it also solidified his front-runner status for the Governor’s race in 2010. California voters increasingly support marriage equality, and the right-wing anti-gay initiative on the November ballot now gives Newsom the opportunity to wage a statewide campaign. Unlike in the 1990’s, Democrats reward politicians who stand on principle – and by June 2010 will view Newsom as one who did the right thing when it was not popular. Newsom’s potential rivals – Los Angeles Mayor Antonio Villaraigosa and Attorney General Jerry Brown – cannot lay such a claim, and will be “old news” by the time 2010 rolls around.

Newsom’s decision on February 12, 2004 – barely two months after winning a very close Mayor’s race – was one of the most brilliant political moves in years. It forced San Francisco progressives overnight to re-think their opinion about him (regardless of their differences with Newsom on economic issues), and it sealed his re-election in 2007. While Newsom took heat from the Democratic Party for “costing” John Kerry the White House, even this backlash was a long-term gain – as it solidified his reputation as a liberal Democrat who will stand on principle when the party leadership said “no.”

But regardless of whether it was a calculated move – or simply a willingness to do the right thing – Newsom undeniably helped the case for marriage equality, legally and politically. We would not have gay marriage in California today without it, nor would a growing number of voters support it. A shift from 61% support for Proposition 22 eight years ago to the state being evenly split on the question today cannot be explained merely by demographic changes or voter turnout models. By pushing the issue into the forefront, California voters have had to re-examine their views – and are moving toward equality.

Which is why the anti-gay marriage amendment on the November ballot will be such a boon for his gubernatorial prospects. In recent days, the press has said that Newsom has a “lot at stake” with the right-wing initiative – and that its passage would hurt him badly. But while the measure is likely to fail (and thus vindicate Newsom again), having it on the ballot is a “win-win” situation for his 2010 ambitions. Like he used Care Not Cash in 2002 as a prelude to running for Mayor, Newsom now has the chance to elevate his statewide profile – and build a grassroots infrastructure for his run for Governor.

But unlike Care Not Cash – where Newsom gained resentment from many local progressives as running for Mayor “on the backs of the homeless” – this time he will work with the Left side-by-side to defend the rights of gays and lesbians. It will earn him enough good will among grassroots Democratic activists throughout California that they will gladly sign up in 2010 to support his run – regardless of the measure’s ultimate fate.

Newsom will also benefit from the fact that Democrats increasingly support candidates who say that the Party should stand on principle – rather than engage in the politics of triangulation. Dianne Feinstein and Gray Davis won the Democratic nomination for Governor in 1990 and 1998, respectively, because they campaigned as moderates who “know how to win” – and primary voters went along with their shameless pandering on the death penalty. But George Bush and the War in Iraq changed how Democrats think – and they’re now upset at a party leadership that is weak, centrist and ineffectual.

By June 2010, these voters will reward Gavin Newsom for being ahead of his time. He was willing to stick out his neck for marriage equality, was shunned by the party elders, but did the right thing by changing hearts and minds. Los Angeles Mayor Antonio Villaraigosa and Attorney General Jerry Brown will also campaign as progressives, but neither can clearly point to a willingness to buck the trend on such a high-profile issue.

Villaraigosa was an early favorite for the nomination with his background as a union organizer. But his fights with the L.A. teachers union – coupled with Newsom’s support for the S.F. hotel workers – will convince organized labor not to go all-out for him as “their” candidate. He also still has to run for re-election in 2009, and his campaigning for Hillary Clinton (far more active than Newsom) has soured his progressive reputation.

Jerry Brown has a much longer record than Newsom of “going against the grain,” but his quirky personality will turn people off as strange. Brown will be 72 by the time 2010 rolls around, and nobody will see an ex-Governor as new and exciting. Brown may have been an innovative progressive long ago, but his tenure as Mayor of Oakland showed how he’ll betray the Left – and that it’s impossible to really know what he stands for.

With his move to issue marriage licenses to gay and lesbian couples vindicated by the state Supreme Court, Newsom can now focus on defeating the constitutional amendment on the November ballot. And once that battle is fought, his front-runner status as the next California Governor will be confirmed.