Donald is the one who closed that door.
He did. But, in Reality Show World, the key is the plot twist that no one sees coming.
I'd say they are both at fault, and equally so. I heard Laura Ingraham last night, and she rightfully said they both need to stop making the attacks so personal. They're both at fault.
An alliance does seem pretty unlikely with the nasty statements of both, but Kennedy got Johnson, and Reagan chose Bush, so stranger things have happened.