I think he can, but I certainly don't think he will. So far he seems to be a terrible general election candidate, and it's hard to see that changing in the next 90 days. It also seems impossible for him to make up the advantage Clinton will have in advertising and the ground game. Even if he does somehow fix those disadvantages, he'll have a tough time getting to 270; it's hard to see Pennsylvania, New Hampshire, Colorado, Virginia, Wisconsin, Michigan, Minnesota, or Oregon voting for him. It also seems that presidential elections
rarely change dramatically after the conventions.