Another member of the White House staff has tested positive for coronavirus.
Andrew Giuliani, the son of Donald Trump's personal lawyer, Rudy Giuliani, and himself one of Donald Trump's aides has said he is isolating with "mild symptoms".
Mr Giuliani, 34, said on Twitter: "This morning, I tested positive for COVID-19.
"I am experiencing mild symptoms, and am following all appropriate protocols, including being in quarantine and conducting contact tracing."
Several White House staffers have tested positive for the disease in recent weeks, including chief of staff Mark Meadows and Trump campaign adviser Corey Lewandowski, while six members of Congress have tested positive this week.
Three lower-level White House aides have tested positive for COVID-19 in recent days, NBC has said.
Mr Giuliani, a special assistant to the US president, was at a news conference at the Republican National Committee's headquarters on Thursday.
The event, at which his father suffered what appeared to be a hair dye malfunction, lasted nearly two hours.
Rudy Giuliani sweated profusely and seemed to have black dye running down his face as he pushed the president's claims that Joe Biden only won because the ballot earlier this month was "rigged".
He repeatedly wiped his brow and cheeks.
The elder Giuliani and other Trump campaign lawyers spoke without masks from an indoor podium to an audience of dozens.
In another blow to Mr Trump's remote chances of overturning the result, Georgia, one of the states where Mr Trump claims fraud occurred, certified Mr Biden's victory on Friday.
Rudy Giuliani, who was a widely-respected prosecutor and mayor of New York before he began working with the Trump team, is currently leading a team of five lawyers fighting to overturn the result of the election.
More than 250,000 people have died after catching coronavirus in the US, more than any other country in the world.