A senior Republican official in the US state of Oregon has quit the party after 40 years and defected to their Democratic rivals because of the “misogyny” and “racism” in Donald Trump's administration.

Lori Stegmann said she stood in opposition to the "unethical and immoral behaviour” of the US leader's White House.

The small business owner and insurance agent who was elected to serve as Multnomah County commissioner since 2016, insisted it was not her that had changed but the Republican Party.

Describing herself as a political moderate, she said the Democratic Party was a “big tent party.”

She told The Oregonian newspaper that she could not "condone the misogyny, the racism, and the unethical and immoral behaviour of the current administration."

She added: ”I have not changed, but the Republican Party most certainly has”.

Donald Trump’s controversial “zero tolerance” immigration policy of splitting families at the US-Mexico border – which sparked bipartisan criticism and international condemnation - was another decisive factor in prompting her to switch sides, she said.

Between 5 May and 9 June of this year more than 2,000 children were separated under the scheme, according to the Department of Homeland Security.

Ms Stegmann – who registered as a Republican when she was 18 years old - was born in South Korea and adopted by American parents but is now a naturalised citizen.

She said Mr Trump's portrayal of immigrants as dangerous to the American economy was “false”, adding: "I think people need to see we are all immigrants”.

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Despite the fact all seats on the county commission are non-partisan, she said the decision to change parties was imperative to her personal values.

“This decision is about who I am, what I believe in and my core values. And if you don't stand for something, then you stand for nothing,” she said. "I prefer to stand. And now I stand with the Democrats."

Addressing her decision to jump ship in a Facebook post, she argued the US president had “emboldened” a “dark side” of America.