Meg Whitman, the chief executive of Hewlett Packard and prominent Republican fundraiser, revealed that she is placing “country before party” and backing Hillary Clinton for president.

The Silicon Valley billionaire’s endorsement of the Democratic nominee comes as a blow to the Trump campaign as it is embroiled in multiple controversies and struggles to retain support within the GOP.

In the past week, Donald Trump has suggested a foreign power hack his opponent, been involved in a public feud with the family of a slain soldier, and refused to back leading Republicans in their reelection bids.

This may prove advantageous to Ms Clinton, who is reportedly working to earn the support of Republicans with significant influence, such as Ms Whitman.

“I will vote for Hillary, I will talk to my Republican friends about helping her, and I will donate to her campaign and try to raise money for her,” she told the New York Times in a Tuesday interview.

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Ms Whitman said that Ms Clinton called her and asked for her support a month ago – although she did not immediately agree to back her. She also confirmed that she will be donating a “substantial” amount to the Democrat’s campaign, despite disagreeing with her on several policy issues.

“I don’t agree with [Clinton] on very many issues,” she said, “but she would be a much better president than Donald Trump.”

Ms Whitman, who has likened Mr Trump to Hitler and Mussolini in the past, called the New York billionaire “a dishonest demagogue” who will lead the US on “a very dangerous journey”.

“Time and again history has shown that when demagogues have gotten power or come close to getting power, it usually does not end well,” she said.

Ms Whitman, who formerly served as chief executive of eBay, unsuccessfully ran for governor of California in 2010, spending $140m (£105m) of her own money on the campaign. She has close ties to Republican nominee Mitt Romney and raised significant funds for his 2008 run for the White House.

She chaired the finance team of Chris Christie’s failed presidential run before he dropped out and devoted himself to Mr Trump. Ms Whitman called the New Jersey governor’s endorsement of Mr Trump an “astonishing display of political opportunism”.