Immigration and Customs Enforcement is a federal law enforcement agency, its agents are peace officers. If they bust down the doors of a house suspected to be full of illegal immigrants and instead find a US citizen wanted for bank robbery, they will effect an arrest and hand him over to local police or sheriff’s deputies. They don’t stay out of it just because it isn’t in their mandate.
Thus if Tom Homan really thinks that Congresswoman Alexandria Ocasio Cortez is aiding and abetting there’s not a lot stopping him from ordering ICE agents to arrest her on probable cause for interfering with federal law enforcement or obstructing justice or whatever. If he’s tired of answering this question and reluctant because a judge is going to pretty much immediately determining the arrest was bullshit and order her released well then that’s his problem and he shouldn’t have sounded like such a fucking Nazi by claiming she was breaking the law.