It’s not Trump who burnt those bridges. The bridge between the grassroots and the establishment was torched by the latter to prevent the former from crossing it to have input in policy. The GOPe wanted all the power for itself, but it is the grassroots on which the party’s success really depends - the establishment is wholly expendable.
Cruz “burned bridges” when he snuggled into bed with the GOPe when he saw he could not compete on his own...His whole “outsider” shtick flew out the window when he sold out to them...