The instant-runoff bandwagon gains another passenger. Nice to see Globe columnist Eileen McNamara jump on the bandwagon today in writing that the instant runoff would make it oh-so-much-easier for liberals to choose between Democrat Shannon O'Brien and the Green Party's Jill Stein. (Click here, here, and here for my past bleatings on the issue.) Give Eileen a comfy seat -- there's plenty of room up here!

Here's how the instant runoff would work in the Massachusetts gubernatorial race. There are five candidates on the ballot. You would rank them in order of preference, one through five. Or you could cast a vote just for the one candidate you like. Or you could choose a first and a second, and leave it at that. The likely result in Massachusetts is that a lot of liberals would vote for Stein first and O'Brien second. A few anti-tax, pro-gun extremists on the Republican side might vote for Libertarian Carla Howell first and Republican Mitt Romney second. (Sorry, Barbara Johnson, but I cannot envision any scenario under which the instant runoff would help you.)

What's great about the instant runoff is that you could give your first vote to the candidate you really want and the second to the candidate you could live with. As it stands now, of course, every vote for Stein is essentially a vote for Romney. With the instant runoff, if Stein didn't actually win, her votes would go to whoever her supporters had designated as their second choice. In most cases, presumably, that would be O'Brien. And if it turned out that O'Brien's margin of victory had come from Stein supporters, then O'Brien would have a powerful incentive to tend to her liberal wing as governor.

It's easy to imagine how two recent presidential races would have turned out differently if the instant runoff had been in effect. In 2000, many of Ralph Nader's supporters would almost certainly have designed Al Gore as their second choice, ensuring Gore's victory. And just to show that this doesn't always go one way (that is, to the left), in 1992, I'll bet that a majority of Ross Perot voters would have marked George Bush the Elder as their number two, thus depriving us of a Bill Clinton presidency for another four years (at least).

Of course, there are unintended consequences to everything, and it's easy to think of a big one if the instant runoff were to become a reality. There's something about the winner-take-all system that forces voters to think like adults -- to put some real effort into deciding not just who they find the most likable or ideologically compatible, but who is actually the most capable of doing the job. I can foresee ways in which the instant runoff would trivialize voting, in which people would designate a fringe or protest candidate as number one and a more serious candidate as number two. Too much of this behavior and the fringe candidate might actually win. Again, consider Stein and O'Brien. If you think Stein would actually be a better governor than O'Brien, well then by all means you should vote for Stein. But if you really think O'Brien would make a more able, competent governor, then it would be frivolous to vote for Stein as your first choice and O'Brien as your second for the sole purpose of sending a message to O'Brien.

Give the instant runoff a try. But let's not assume it's going to be the answer to all of our problems.