There are over 3 years of evidence that he is not.
And over 15,000 of his lies have been documented and debunked (as at 16 Dec 2019, according to Washington Post, who is tracking the number of lies he has told. Update: Link to archived WaPo page provided by commenter. Thanks Mich.).
Here is just one example of Trumpslaining and the DunningKruger Effect:
"US president Donald Trump has argued with his US trade chief during a televised trade meeting. When asked a question about trade talks with China, which have been taking place over the weekend, Donald Trump said he is against using memoranda of understanding [MOUs]. ‘I don't like MOUs because they don't mean anything. To me they don't mean anything,’ Trump said. Robert Lighthizer jumped in to explain that an ‘MOU is a contract … a binding agreement between two people’. To which a gruff Trump replied, ‘I disagree.' Lighthizer got the message, adding ’from now on we're not using the word Memorandum of Understanding anymore. We're going to use the term trade agreement, all right?’"
"Stupidity is like being dead. It creates problems for others. But there is no problem for the stupid and the dead."