Elon Musk and Peter Navarro.Elon Musk slammed US President Donald Trump’s trade adviser Peter Navarro as “truly a moron” and “dumber than a sack of bricks” on Tuesday. Musk’s insults came in response to Navarro’s comments made on Monday on CNBC about Tesla’s manufacturing practices, in which Navarro referred to Musk, Tesla’s CEO, as “not a car manufacturer” but “a car assembler” while arguing that the car company depends heavily on foreign supply chains for items such as batteries. Now, Musk, who’s overseeing federal spending cuts under Trump, has fired back at Navarro’s claims.