Dr Anthony Fauci, the U.S. government’s top infectious diseases official, self-quarantined on Sunday.
This development happened after two White House staff tested positive for coronavirus.
Fauci, 79 has begun what is being described as “modified quarantine”.
It involves some work from home, social distancing and wearing a mask.
However, he is scheduled to testify in Senate next week.
Fauci is not the only person on Trump’s COVID-19 task force in contact with a confirmed case of coronavirus.
Two other senior leaders in the Trump administration’s fight against Covid-19 were also self-quarantining on Sunday.
One of them is Dr Stephen Hahn, commissioner of the US Food and Drug Administration.
The other is Dr Robert Redfield, director of the Centers for Disease Control and Prevention.
Both have gone into two weeks of isolation.
News that three core members of the US pandemic task force were having to go into some degree of self-isolation could not come at a worse time for Donald Trump.
The president is trying to project an image of confidence and resolution as he encourages states to reopen their economies.
Simultaneously, his administration is proving unable to keep the virus at bay even within the White House.