Under different circumstances, New York Mayor Mike Bloomberg could have been running for president this fall. It's no secret that he considered running as an unaffirliated contender who would speak blunt truths.
But Bloomberg didn't run. So, like most other Americans, he was faced with "the choice."
Sure, Bloomberg's a social liberal, like President Obama -- only more aggressive, particularly on gun control and public-health initiatives that don't make fast-food chains or sugary soda pop producers all that happy.
But he's also a businessman-turned-politician, like Mitt Romney -- only much more successful in business, and in all likelihood more successful in politics.
So where would the Republican-turned-Independent mayor of America's largest city -- and one of the few reasonably well regarded unaffiiated political players -- go?
And for exactly the right reason.
Obama he argues "gets" it that climate change matters.
Romney does not -- or, at the least, does not want to say it matters because he fears the climate-change deniers in his own Republican Party.
As a campaign where both major-party candidates neglected climate change as the front-and-center issue it should be, the east coast was hit by the second epic hurricane in as many years.
That, Bloomberg determined, was a tipping point.
He looked at the candidates and recognized: "One sees climate change as an urgent problem that threatens our planet; one does not. I want our president to place scientific evidence and risk management above electoral politics."
That does not make Obama a perfect candidate in Bloomberg's eyes, even on questions of global warming. And the mayor's association with Obama certainly does not make Bloomberg a perfect player; his stances on education policy, civil liberties and economic justice in New York City still merit scrutiny and objection.
But with his endorsement of Obama, Bloomberg has done something vitally important.
He has called for an issue-based vote, a science-based vote. As he put it in issuing what could be the most notable endorsement of 2012, Bloomberg wrote that he would cast: "A Vote for a President to Lead on Climate Change."
Here is how the mayor explained his unexpected decision:
"The devastation that Hurricane Sandy brought to New York City and much of the Northeast -- in lost lives, lost homes and lost business -- brought the stakes of Tuesday's presidential election into sharp relief.