You think Antifa are "anyone they don't like?"Because empowering the politicians and government bureaucrats to declare anyone they don't like a "domestic terrorist" is exactly how you become England.
Clearly you have not been paying attention.
They are well-organized, well-funded, domestic anarchists who are using fear, rioting, murder and political blackmail to try to overthrow our form of government and install a socialist regime based on Marxist principles.
Domestic terrorists indeed.
Now the Patriot Act did offer a definition of what a Domestic Terrorist is, however this has not yet been challenged in court and is not likely to stand up.
I can guarantee you that the Trump administration has traced funding for Antifa to organizations outside the US - likely Soros funded organizations located outside the US to avoid scrutiny by the IRS - and THIS ALONE defines these groups as externally funded and qualifies they as International Terrorist organizations.