The "death penalty for drug dealers" play, is simply about optics. And its very good optics. It's a persuasion play to stake the position as being the strongest on this particular policy, while knowing full well it'll likely never happen. These sentencing decisions are almost entirely made at the level of state law. They're not enacted by the executive branch (POTUS or Governors), would need legislatures to pass them and likely wouldn't survive court challenges. But to the average voter, it creates an impression the politician is taking the toughest stance possible on a problem.