Consider Mitt's father role in getting Barry Goldwater's campaigned destroyed. Consider that Mittens was behind Evan Mullen's 2016 campaign that was publicly stated as being for the sole purposed of stealing votes from Trump. Consider how often Mitt goes against Trump for no logical reason.
Obama getting re-elected for a second term was very important for reaffirming his place in history. Who better then to select as an opponent than someone that is uniquely qualified when it comes to throwing a fight?
I didn't like Mitt, didn't vote in 2012. I can't remember how much of a fight he put up. Did he put up a fight? Or did he take all the abuse? Makes me wonder.
Looking back at that election.. just holy shit. I honestly think a romney presidency wouldve been even worse than obama. At least with obama you knew he was the bad guy.