Huge mistake. George Washington was specific in accepting his salary because he knew he was setting examples for the future. He feared that if he did not accept his salary no one after would either and that would keep qualified persons from running for president.
So, if Trumps actually does this, where no one prior to him has, even the Roosevelts, then what does that say for the next president? This is a mistake. He should accept the money and donate $400,000 to the charity of his choice.
Herbert hoover is the only other president to not accept his salary. Others have taken* it and given it to charity and then deducted it from their taxes which technically is taking +the money. ..but it looks good and generous. No fanfare Trumps way.