The autopsies to be performed on the Romney campaign will be abundant yet varying in their assorted summations. But in the end, it was the nominee's lying that did him in. Cause of political death: lethal mendacity.
This assumes that Romney ever had a reasonable chance of survival. From the beginning I have argued that he did not, principally because of President Obama's enduring popularity as well as the equal conspicuity that the GOP's real heavyweights--Daniels, Christie, J. Bush--chose, early on, to postpone their glory days till 2016. Each of these potential contenders knew how to read an electoral map. Nonetheless, exceedingly capable presidential nominees can bend the arc of destiny (e.g. Truman '48); and given the right approach, it was never impossible for Romney to do just that.
So what was the wrong approach? The erstwhile Rovian theory that the Republican base alone could carry a presidential election. To virtually every political observer's surprise, Romney persisted in pumping the base well after he had effectively secured the nomination. My guess is that Romney continued pumping the base not so much because he feared partisan defections, but because he felt compelled to turn out almost exclusively the true believers on Election Day, who would, or so his advisers told him, constitute a slim majority.
And what single cement unified this partisan body of believers? You got it. A seething detestation of Barack Obama. And what better way to whip up hysteria and mobilize the rabble than to propagate outrageous lies, from "apology tours" to welfare giveaways to ObamaCare "ending Medicare as we know it" ... nearly ad infinitum.
Romney & Co. spotted its grossly mistaken calculation too late. Only in October did the nominee dramatically correct his doomed course by careening to the middle and blathering about compromise and bipartisan cooperation. Incompetent stumblebum that he is, though, when Moderate Mitt failed to move Ohio's numbers, he doubled down--again--on the lies, this time on the auto bailout.
And so Romney goes out as he came in: immensely lying his little ass off. And in the end--indeed, from the beginning--that's what got him.