Seattle, Washington - American philanthropist Melinda French Gates, the ex-wife of Microsoft co-founder Bill Gates, endorsed President Joe Biden on Thursday for November's election, arguing that he is the best candidate for women.

"I've never endorsed a presidential candidate before. But this year's election stands to be so enormously consequential for women and families that, this time, I can't stay quiet," she said on X.

"Women deserve a leader who cares about the issues they face and is committed to protecting their safety, their health, their economic power, their reproductive rights, and their ability to freely and fully participate in a functioning democracy."

French Gates, who recently stepped down as president of the Bill and Melinda Gates Foundation, said the contrast between Biden and his Republican opponent Donald Trump "couldn't be greater, and the stakes couldn't be higher."

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"I will be voting for President Biden," she concluded.

Reproductive rights have been an effective political cudgel for Democrats in the two years since the conservative-majority Supreme Court overturned Roe v. Wade, the landmark 1973 decision that made abortion a constitutionally protected right.

A comfortable majority of Americans think abortion should be legal in most cases, according to extensive polling, and around half of states have measures in place to protect access.

The issue has been a major theme of the election campaign, with Biden supporting women's right to choose and Trump failing to stake out a clear-cut position beyond pride in appointing three of the justices who struck down Roe v. Wade.

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French Gates announced in May that she would be using her $12.5 billion fortune to help "women and families," making a first payment of $1 billion toward the cause.

She said the Supreme Court ruling on abortion had prompted her to devote herself to defending women's rights.

Former New York mayor and businessman Mike Bloomberg also said on Thursday he was endorsing Biden and had donated $19 million to his campaign, according to the Washington Post.

Trump, meanwhile, received high-profile support from investor twins Cameron and Tyler Winklevoss, who announced they had each donated $1 million toward the Republican candidate's election bid.

And businessman Timothy Mellon contributed $50 million to a Trump-supporting super PAC – an organization that pools campaign contributions, according to a New York Times report on Thursday.