February, Mr Trump said reports that Mr Mulvaney would be fired were "false", insisting he had a "great relationship" with him.
Who is Mark Meadows?
Mr Trump's new chief of staff is a close ally of the president with a record of supporting hardline conservative causes and climate change denial in the US.
In 2012 he publicly embraced the conspiracy theory that President Barack Obama was not born in the US but instead in Kenya.
As head of a group of conservative politicians called the Freedom Caucus, Mr Meadows lobbied the White House to close down the government's climate change office.
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