#1 Publicly apologize for all those he has attacked; i.e., Cruz, Kelly, Carson, Bush, Latinos, military, blacks, women, etc., and then and perhaps most importantly #2 He needs to stand down and drop out of the race for the good of the country and explain to his supporters that he is doing so for the good of the country. #3 Emphatically endorse Pence and vow to campaign for him
IF he were to do those things he may just garner some respect for those who strongly oppose him.