The Electoral College, the system used for more than 220 years to pick American presidents, has been under siege since George W. Bush beat Al Gore to the White House despite losing the popular vote.

On Monday, California added its substantial clout to a movement to overturn it.

Calling election by popular vote "basic, fair democracy," Gov. Jerry Brown signed legislation backing an interstate compact to award the state's electoral votes to the candidate winning the most votes nationwide, regardless of which candidate California voters choose.

The bill would take effect only if states controlling a majority of the nation's electoral votes agree.

But California's endorsement — and the commitment of its 55 electoral votes — provided the effort its most substantial lift yet. Now, eight states and the District of Columbia have adopted the agreement, representing almost half of the electoral votes proponents need.

"We just try to push the noodle along every year in every state where we can push it along," said John Koza, the Los Altos Hills computer scientist who founded the National Popular Vote project in 2006.

California's backing, he said, "gives it the credibility so that it's not just a theoretic or academic idea."

Proponents of the popular vote movement say it would make California, a safe Democratic state, more relevant in presidential politics.

The bill's author, Assemblyman Jerry Hill, D-San Mateo, said in a written statement that Californians are ignored by candidates "pandering exclusively to the battleground states," and Brown referred to the state's lack of prominence when signing the bill.

"California should not be taken for granted in presidential elections, and it seems logical that the occupant of the White House should be the candidate who wins the most votes," Brown, a Democrat, said in a prepared statement. "That is basic, fair democracy — and that's why California has joined the movement for a National Popular Vote."

The Electoral College's defenders say it keeps candidates from ignoring small states and rural areas, and the legislation, Assembly Bill 459, passed through the Legislature with little Republican support. Brown's predecessor, Republican Gov. Arnold Schwarzenegger, said when he vetoed previous versions of the bill that the plan was "counter to the tradition of our great nation, which honors state rights."

Schwarzenegger also said he could not endorse awarding California's electoral votes to a presidential candidate a majority of Californians may not support.

Sen. Doug LaMalfa, R-Richvale, said in a written statement Monday that the bill Brown signed rejected "American tradition that protects the fabric of our country from fractionalization and mob rule."

Koza pointed to Republican support in the New York Legislature as evidence of bipartisan support. But the list of states currently supporting the measure, including Vermont, Massachusetts, New Jersey and Illinois, "sounds kind of like an MSNBC viewing party," said Bill Whalen, a research fellow at Stanford University's Hoover Institution and former speechwriter for Gov. Pete Wilson.

"The question here is what, if any, red states are going to jump into this," he said.

Justin Levitt, an elections law professor at Loyola Law School in Los Angeles, said the measure isn't sure to benefit Democrats. In a reliably blue state like California, he said, Republicans might find their votes matter much more.

"The states that have signed on so far certainly tend to be overwhelmingly Democratic, but there are some pretty prominent Republicans that have endorsed the proposal," he said.

How quickly it could happen, if at all, is unclear. Koza said he has been lobbying for the system since 2006 and believes it could be in place for the presidential election in 2016.

If the system is enacted, Levitt said, how presidents are elected "would change rather remarkably." He said, "Big, large-scale national changes like this always take time."

California, like all other states but two, commits its full slate of Electoral College votes to the candidate who receives the most votes statewide. Nebraska and Maine allocate most of their electors by congressional district.

The Electoral College, largely ignored by most Americans for years, gained widespread attention during Bush's election in 2000. It remained a focal point four years later, when Bush won the popular vote and re-election but nearly lost the Electoral College to John Kerry.

Before Bush's victory in 2000, just three presidents had won election without carrying the popular vote, the last one Benjamin Harrison in 1888.