It can be rejected but not undone. If they guy says he supports you are you going to call him a liar? My quibble is with the English here and the effect of words. You can repudiate all you want but only the one who says I support you can undo it.
Any endorsement can be rejected. Rejected means rejected. The only people arguing about how many angels can dance on the head of a pin are Cruz supporters. Splitting hairs to a ridiculous degree is all they have left.
Btw, I wish I had a dollar for every time a Cruz supporter said, ‘’Trump isn’t the nominee yet. Cruz will support him when he’s the nominee.’ I’d buy an annuity.