Those people have real problems that I am sympathetic to. For example, being left behind economically. Problems at the border. etc. Trump speaks to these problems and the democratic party does not fix these problems.
The reason Trump is popular is because he is willing to lie and make false promises in order to gain support. Any one can do this, you just have to have no moral boundaries and some charisma. For example how Enron, Theranos, and that crypto guy are able to defraud billions of dollars from investors.