First, it makes Trump look like a tyrant to the soft democrat - independent middle -soft republicans. Second, there are plenty of rock ribbed conservatives who are staunch Constitutionalists. Federalist Society leapd to mind.
When Trump tweets from the hip - without thinking things through - he often comes off as a twit. He'd his own worst PR enemy.
There are no fence sitters this election. People already know who they are voting for this election.