President Trump 's all but down for the count in his battle with Special Counsel Robert Mueller ... so says " The Blacklist " star Harry Lennix .

We got Lennix at LAX and asked him what he thought about Trump saying "We'll see what happens" when asked if he'll allow Mueller's investigative team to interview him. Remember ... Mueller has spent 8 months looking into whether Russia interfered with the 2016 U.S. Presidential election.