A good comparison

As Axios explains about the Trump tweet saying that "Antifa" will be designated a terrorist organisation:  

Mark Bray, author of "Antifa: The Anti-Fascist Handbook," wrote of Trump's tweet: "To explain a little: it's like calling bird-watching an organization. Yes, there are bird-watching organizations as there are Antifa organizations but neither bird-watching nor antifa is an organization."

It seems that some in the White House see the pointlessness of the idea, but populists Right wingers thought that it was a good idea:

As recently as Saturday night, senior administration officials told me that the designation of a violent cohort of far-left activists, antifa, as a terrorist organization was not being seriously discussed at the White House. But that was Saturday.

Behind the scenes: The situation changed dramatically a few hours later, after prominent conservative allies of the president, such as his friend media commentator Dan Bongino, publicly urged a tough response against people associated with antifa (short for "anti-fascist").

It's just throwing red meat to Trump's ignorant base - I see Australia's stupid Trumpists are putting up Red State posts theorising about how effective such a declaration could be.