Draining the swamp.
If you look at his cabinet, he repeatedly picked the most establishmentarian, corrupt hacks to flock around him and gave clemency to idiots who hated him and wanted his agenda to fail, like Mitch McConnell, William Barr, and "General" Milley. If there's a grain of truth to the "AKSUALLY TRUMP CAUSED THE AFGHAN FIASCO" argument, it's that by allowing the generals to deceive and backstab him, he guaranteed the incompetent louts could continue to act as they had in the past 20 years... that is to say, without a shred of care for victory or the lives of US citizens and soldiers. He also allowed them to whisper in his ear, and pick a dud of a Supreme Court nominee, ACB.
I say all this because I truly think Trump's heart and instincts are in the right place. But if there's one reason I'm hesitant to see him be President again, it's that he really hasn't corrected this great flaw of his. If he does, though, then growth can really begin.