His supporters do one of three things, or a combination of the three.
1.) They scapegoat and then use that to justify his actions. Example: "Oh ya well Person A did X at Y time so obviously that excuses Trumps Z action now."
2.) They use deflection mental gymnastics techniques to explain away why he does what he does. Example: "Well Trump never really meant to do X, he was never being serious about it because I knew what was in his heart. Why does your Person A do random (y), clearly that's the real problem.
3.) They dismiss dialogue by retreating to their side of the playground. Example: "Quit whining, he won you lost."