No, Obama and his media sycophants killed Romney. Romney did his share by listening to consultants which exposed his poor campaigning skills. but in the end Romney was trashed by a campaign showing him to be a heartless corporate rich guy who kept women in a notebook, gave up on 48% of the people who wouldn't vote for him, and even had an elevator for vehicles in his two-story garage. Obama is probably the best campaigner we had, better than WJC, and mobilizing and exciting people to vote. He was so good at it, that is how he governed. Everyone gripes about negative campaigning, but it works. In a sense Obama and Trump are two sides of the same coin, but Obama is much more elegant with his trash talking.
Oh and you can stop with your Romney would have been a good president baloney. I agree, he had demonstrated considerable skills and knowledge that placed him way ahead of his 2012 opponent, but you never believed that.
Romney had some self-inflicted wounds. I was very interested him in the GOP debates. But everything Romney said in the primary was "Forget all those things I did as governor, I will not do any of them as president. As president I want to slash taxes and spending and I'll never talk to a demoCRAT". That wasn't his MA story. He know "yep, what I did by cooperating and seeking a balanced approach worked and I'll do it as president" would lose him the primary. So he made a choice that hurt him in the general.