Mr Trump also asked all Americans to wear face coverings, saying "they'll have an effect" and show "patriotism".
The president, who was not wearing a mask at the briefing, has previously disparaged them as unsanitary.
His aides have reportedly pressed him to adopt a more measured approach as virus caseloads spike across the US.
The daily White House news conferences ended soon after Mr Trump suggested in April during freewheeling remarks from the podium that the virus might be treated by injecting disinfectant into people.
In his first White House coronavirus briefing for months on Tuesday, a less off-the-cuff president echoed what public health officials on his pandemic task force have been saying as he warned: "It will probably unfortunately get worse before it gets better.
"Something I don't like saying about things, but that's the way it is."