Amazon billionaire owned influential newspaper, The Washington Post, has said it will endorse neither Kamala Harris nor her Republican opponent Donald Trump in the upcoming US presidential election 

In a statement released on Friday, the paper's CEO William Lewis said this was a return "to our roots of not endorsing presidential candidates."

However, the Post editorial board has endorsed candidates for much of the last four decades — all of them Democrats — before deciding to stay on the sidelines in one of the most polarising elections in US history.

Newspaper editorials have little of their once-powerful political heft. But the Post — whose slogan is "Democracy dies in darkness" — is one traditional media outlet that retains influence among Washington's elite.

Trump's campaign quickly pounced, crowing that "Harris is so bad, The Washington Post decided to never endorse another presidential candidate again."

The Washington Post Guild, which represents unionised staff at the newspaper, said it was "deeply concerned."

"We are already seeing cancellations from once loyal readers," a statement said.

US media reported that a senior Post figure, editor at large Robert Kagan, had resigned in protest.

Billionaire owners

The Post's decision follows a similar move by another of the big remaining US newspapers, the Los Angeles Times.

The billionaire owner of the Times blocked the editorial board from issuing an endorsement for Harris, according to editorial editor Mariel Garza, who resigned in response on Wednesday.

According to a report by The Washington Post on its website, Bezos likewise intervened to block the board from publishing its editorial in favor of Harris. However, a source close to the Post's leadership told AFP that this "is inaccurate."

By contrast, The New York Times endorsed Harris in September, calling her "the only patriotic choice for president" and warning that "it is hard to imagine a candidate more unworthy to serve as president of the United States" than Trump.

On Friday, Harris also scored the backing of The Philadelphia Inquirer, the biggest newspaper in swing state Pennsylvania, which declared that "voters face an easy but tectonic choice."

The Republican got his own boost Friday from the New York Post, the Rupert Murdoch-owned tabloid, which declared that "America is ready for today's heroic Donald Trump to reclaim the presidency."

'Cowardice'?

In a statement, The Washington Post's Lewis wrote that the paper would not make presidential endorsements again.

"Our job at The Washington Post is to provide through the newsroom non-partisan news for all Americans, and thought-provoking, reported views from our opinion team to help our readers make up their own minds," he said.

The Post has been endorsing Democratic candidates consistently as far back as the 1980s, always making clear that the editorial board works separately to the newsgathering operation — as is typical in US news organisations.

The Post's former executive editor, Marty Baron, lashed out at the daily's "cowardice, with democracy as its casualty."

Baron said that Trump would see the decision "as an invitation to further intimidate" Bezos.