MICHIGAN, Dec. 14 (CNA) - Democrat Joe Biden on Monday (Dec 14) won the state-by-state Electoral College vote that formally determines the US presidency, all but ending President Donald Trump's floundering campaign to overturn his loss in the Nov 3 election.

California, the most populous state, delivered its 55 electoral votes to Biden on Monday afternoon, officially putting the former vice president over the 270 votes needed to secure the White House. Based on November's results, Biden earned 306 Electoral College votes to the Republican Trump's 232.

Earlier in the day, electors in several major battleground states where Trump has unsuccessfully sought to reverse the outcome - Arizona, Georgia, Michigan, Nevada, Pennsylvania and Wisconsin - also voted for Biden, who is set to take office on Jan 20 alongside running mate Kamala Harris.

Traditionally a formality, the Electoral College vote - set for Monday by federal law - assumed outsized significance because of Trump's unsubstantiated claims of widespread fraud.

There was next to no chance that Monday's voting would negate Biden's victory and, with Trump's legal campaign to reverse the results failing, the president's dim hopes of clinging to power rest with persuading Congress not to accept Monday's electoral vote during a Jan 6 special session - an effort that is virtually certain to fail.

Once in office, Biden faces the challenging task of fighting the coronavirus pandemic, reviving the US economy and rebuilding relations frayed with US allies abroad by Trump's "America First" policies.