It's security theater, just like airport security screening. The politicians need to be seen doing something.
Don't look into yourself and see what can be fixed, always blame the other.
Unfortunately this kind of measure is going to increase the R0 of the virus, because some people will think "oh I see, the virus is over there, and now the president has closed off that vector."
I can't even tell if this is supposed to be about Trump. Also it doesn't matter.
There are thousands of borders and even more politicians on this planet and if you don't think borders are the scapegoat for problems the world over, then you're really thinking very small.