By James OliphantWASHINGTON (Reuters) -U.S. President Donald Trump says he will soon declare the anti-fascist antifa movement a domestic “terrorist organization” as part of a crackdown on what he claims is left-wing sponsored political violence. Here is some background on the movement, and why it might be difficult for the Trump administration to follow through on its threatened crackdown:WHY IS TRUMP DOING THIS NOW? Trump vowed to take action against left-wing groups he accuses of fomenting violence after the murder of conservative activist Charlie Kirk earlier this month. Still, Trump has described antifa a “sick, dangerous, radical left disaster” and has vowed to go after its sources of funding. Trump first sought to designate the movement as a domestic terror organization during the George Floyd protests in 2020.