The Secret of Current Trump Support

To me, it's found in this quote in a New Yorker piece on understanding Trump:

“The truth is, virtually everyone who claims to know what Trump is going to do has been wrong at some point,” one sharp analyst told me. “The best indicator, in my mind, is to go back and read his core campaign pledges and speeches. Those have been far more instructive than anyone in Congress, in the Republican Party, or on his own team.”