President Donald Trump defended his latest efforts to crack down on far-left extremism following the assassination of conservative activist Charlie Kirk on "The Story" Thursday.A week after Kirks assassination, Trump wrote in a Truth Social post that he would designate the radical left-wing, anti-fascist antifa group as a "terrorist organization.""It should have been done a long time ago," Trump told Fox News anchor Martha MacCallum.DONALD TRUMP JR. WARNS POLITICAL VIOLENCE IS 'NOT GOING BOTH WAYS' AS HE MOURNS CHARLIE KIRK'S DEATHTyler Robinson, the 22-year-old suspect in Kirks assassination, has been charged withaggravated murder and six other felonies by Utah prosecutors.His mother said Robinson had"become more political," leaning leftand supporting "pro-gay and trans rights," according to court documents.The Kirk assassination suspects casings and unfired roundsinclude the etchings "Hey fascist! Catch!" and "Bella ciao,"a reference to an Italian, anti-fascist anthem sung during World War II.No motive has been confirmed in the investigation. And there is no reported evidence that Robinson is a member of antifa.When MacCallum asked Trump if he believes there is a "vast terrorist movement" that targeted Kirk and well and his life and the lives of New York City CEOs, he replied, "You never know, do you? And well find out, maybe."He went on to call antifa a "sick group.""Its a sick group, very very sick groupThey love burning the American flag," Trump said. "Were going in, and were saying it incites riots, and therefore you go to jail for one year if you burn the American flag."'DARK MOMENT FOR AMERICA': TRUMP DECLARES CHARLIE KIRK'S VOICE 'BIGGER AND GRANDER' AFTER ASSASSINATIONWhile the Supreme Court ruled flag burning is protected by the First Amendment, the Trump administration will argue to courts that the act fuels "incitement of riots," the president explained."Antifa causes tremendous incitement, and the things they say and the things they do are horrible," Trump argued.While Trump maintained he has always been in favor of free speech, he criticized "crazy" reactions to Kirks assassination."I see people saying things theyre crazy," Trump argued. "Maybe theyre drugged out, maybe theyre some other problem."The commander-in-chief praised Kirks "incredible" following, revealing he had told the late Turning Point USA (TPUSA) founder he had a "good chance" of being president one day."He was very compelling," Trump reflected. "Ive never seen anybody capture a group of people like he captured youth."TRUMP EYES REMARKS AT CHARLIE KIRK MEMORIAL IN ARIZONA, BLAMES LEFT FOR SUSPECTS RADICALIZATIONTPUSA unanimously elected Kirks widow Erika to lead the organization as its new CEO."No one will ever forget my husbands name and I will make sure of it," Erika vowed. "My husbands mission will not end, not even for a moment."CLICK HERE TO GET THE FOX NEWS APPErika, Trump, and Vice President J.D. Vance are expected to deliver remarks at Kirks memorial in Arizona Sunday.