It actually makes the Dems overconfident, as they misread how acceptable their policies are to the electorate. Then they find out the hard way that they have lost again.
The typical John Doe voter loves NASCAR and spends his spsre time fixing up old pick up trucks. He's not paying attention to politics but he's on the Trump train. He needs to be reminded to show up to vote on the Election Day.
So he needs constant reinforcement to vote and that is the greatest flaw of Trump's coalition is his dependency on low-propensity voters.