I think he is doing Cruz a favor. He has taken a lesson from the Clintons. If there is an issue that is going to be an issue later, better to get it done with sooner.The Democrats are going to have a screaming fit about it if Cruz becomes the nominee. Better to deal with it now and let it be old news then.
Cruz needs a definitive judgement NOW to be considered as VP.
Trump simply tying-up loose ends so no surprises in the general.