2012? Against the wildly popular incumbent? Blaming it all on smears seems like a rationalization. So the real question is what would have happened if Romney had run in 2016. But we basically know what would have happened, because there were other moderate/conservative candidates who did run in 2016. And the answer to that is the Republican party would have still fallen for the temptation of the New York democrat con artist who paid lip service to their longstanding frustrations but didn't have any actual policy beyond "burn it all down".