Some in the US believe it's unconstitutional: the US wasn't under a direct threat from military action and there was no congressional mandate. Probably not illegal in US law as the Supreme Court has effectively ruled that actions by a President in the course of his duties are above the law. The President is accountable to Congress but, of course, there's no chance of impeachment at the moment but if power shifts after tge midterm elections ...
I was interested in Farage’s response. Does it imply he's in favour of breaking laws if it helps one's cause; could shoplifters claim "it's against the law but I needed that Champagne t celebrate the new year with friends and family to celebrate new year and I didn't have any money left after Christmas" ... a dangerous path to anarchy? (Also similat to an argument "Stop Oil", etc use?)