Trump is and remains a sad puppet of the Congressional GOP leadership. As I've said before, he's the least authentic anti-establishment candidate possible.
And what, exactly, do you think the President can do about legislation that passes both chambers with majorities far beyond those necessary to override a veto?
If he actually believed it was unconstitutional, he'd veto the bill to take a stand and then challenge the law in court. As things stand, he's just whining about nothing.
Never stopped W or Obama from adding their own signing statements to laws they felt were unconstitutional.