Another run would be genuinely frightening for Republicans — and this is probably why the reaction against it has been so intense — if there were any chance of Romney doing what he did in 2012: monopolizing fund-raising to a point where other potentially electable candidates stay out; carpet-bombing his opponents with attack ads; and essentially forcing the party faithful to accept him, flaws and all.

But unless G.O.P. power brokers are truly crazy — and based on the response to Romney’s trial balloon they aren’t — that isn’t going to happen. Not even close. Instead, a Romney candidacy would depend on a small circle of backers while ceding immense fund-raising territory to Jeb Bush, Chris Christie, Scott Walker, Marco Rubio … the list goes on. He wouldn’t quite resemble his old rivals Newt Gingrich and Rick Santorum, each of whose insurgent campaigns were floated by a single megadonor, but he would be closer to their position than to that of the commanding Mitt of old.

And he would resemble Gingrich and Santorum in other ways. In 2008, he had the backing of key voices in the conservative movement; in 2012, he had the establishment (however reluctantly) behind him. In 2016, he would be on his own, hanging out in Iowa living rooms and New Hampshire diners, trying to win primaries on the basis of debate performances and flesh-pressing and even (gasp!) ideas, like any other long-shot candidate.

Which is why, purely as human drama, Romney 3.0 could actually be interesting to watch.