They say that people in the White House report that when Tucker Carlson finally started to tell people that perhaps they needed to pay attention to what the medical experts were saying and that this was not a hoax, that this was an epiphany for Trump. Since then he has started to modify his attitude because this indicated to him that his base, to whom Trump considers Carlson to speak for and to, was no longer willing to accept his previous claims about whether the virus was real or not.
So once again, it took what Trump was hearing on Faux News to determine what HIS administration's positions and policies are going to be.