Withdraw from NAFTA. The rust belt, especially Michigan, view it as their own treaty of Versailles. Trump can virtually guarantee rust belt electors, which also guarantees the election. The farm states might hurt a bit, but they won't vote flip to the enemy.
Strict federal voter ID laws, this would guarantee his election, and get many blue-blueish states either become red or swing states and make red states hardened red. Another thing to consider is mass deportations. If he decides to repeal DACA, a fuck ton of the Dem voting base would be gone. He won't win Cali with it, but it makes congressional races in California a hell of a lot easier.