White House Chief of Staff Mark Meadows has been diagnosed with coronavirus.
Mr Meadows was at the White House party on election night and was seen without a mask.
He has frequently appeared at public events without wearing a face covering and accompanied the president in the final days of the campaign rallies.
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The diagnosis was confirmed on Friday by two senior White House officials.
His current condition and the circumstances of how he may have become infected are so far unclear.
Mr Meadows is the latest of Mr Trump’s inner circle to test positive.
His wife Melania and son Barron also had the virus, as did his national security adviser Robert O’Brien and Mike Pence’s chief of staff Marc Short.