A top aide to US Vice-President Mike Pence has tested positive for Covid-19 one day after another White House staff member was diagnosed with the virus.
Mr Pence's press secretary Katie Miller tested positive on Friday, a day after President Donald Trump's valet.
The White House has begun daily testing for Mr Pence and Mr Trump, and has claimed to be taking "every single precaution to protect the president".
The US death toll is now over 76,000 and states are beginning to reopen.
Six members of Mr Pence's team were abruptly taken off his plane, Air Force 2, after it was held on the tarmac outside Washington, DC for over an hour on Friday, as he prepared to travel to Iowa to meet religious leaders.
The staff members had had recent contact with Mrs Miller, according to an unnamed US official cited in the media pool report. The president and vice-president had not.
Mrs Miller is the wife of Trump aide Stephen Miller.
During a meeting with Republicans at the White House, Mr Trump told reporters: "She's a wonderful young woman, Katie."
"She tested very good for a long period of time and then all of a sudden today she tested positive."
When asked about the possibility of an outbreak in the White House, Mr Trump told reporters: "All you can do is take precautions and do the best you can."
He also said he was correct not to wear a mask while visiting the World War II memorial in Washington for VE Day, because the elderly veterans there with him were "far away".
"Plus the wind was blowing so hard and such a direction that if the plague ever reached them, I'd be very surprised," he added.
BDST: 1304 HRS, MAY 09