Mayor Bloomberg's last-minute announcement of support for President Obama is an endorsement of competent governance.

It is an endorsement that will appeal to Bloomberg's biggest enthusiasts: the political pundits. It is a the loudest reference to climate change this campaign season. And as much as anything, it is an indictment of the political journey of MItt Romney.

Many won't be surprised that New York's mayor would back the president. He is socially liberal, an outspoken advocate of marriage equality and reproductive rights, who has spent considerable money promoting both causes. He is a believer in robust government action - a value more likely to find a home in the national Democratic Party than with the Republicans. His claim to fame is as a business mind, and he must see that the economy has moved the right direction, if not quickly enough, in the past four years.

However, Bloomberg had been claiming a vow of silence. He had publicly reprimanded both candidates over their refusal to take on gun control in a strong, unyielding way. He had just announced a SuperPAC that he was clear would not back a Presidential camp. Bloomberg has himself been talked of as a presidential candidate and has enjoyed his ambiguous partisanship. Staying out seemed to be part of his brand as a non-ideological independent.

So what changed?

On the surface, the events this week surrounding Hurricane Sandy made his choice clear. Under Republicans, FEMA was gutted; under Democrats, it has been rebuilt. Republican leaders decry "big government." Democrats talk about how we prepare for challenges bigger than any individual citizen, city or state. Mitt Romney spent the week setting up photo-ops and running discredited ads. President Obama spent it - like Mayor Bloomberg, Governor Cuomo, Governor Christie and other elected and appointed officials - governing.

Furthermore, as Bloomberg Businessweek announced on its cover: "It's Global Warming, Stupid." While neither candidate campaigned on climate change, one of them has a record of taking sensible steps as President. The other used climate change as a convention speech punchline. Mocking rising water levels, and the earnest effort to address them, is no longer very funny.

Maybe Bloomberg is basing his endorsement on Obama's record which looks similar to Bloomberg's own: willing to take some measures that would be derided as "nanny state" for the public good; a measured approach to employing public and private tools to boost the economy; a comfort with police and security approaches that outrage civil libertarians; socially progressive, though not radical. Obama's record is not a liberal agenda, by any means, but one that resembles the Mayor's.

Or maybe Bloomberg's endorsement is an investment in a discussion of climate change. It's his way of saying that sensible, business-minded, independent-branded, cross-partisan aspiring, centrist-sounding, non-ideological, good-governance technocrats care about what we're doing to the earth and believe we can do better. It's Bloomberg's way of endorsing not just a candidate, but an issue, and elevating it for the next four years.

And just as likely, Bloomberg's announcement is a condemnation of the right-wing gravitational pull that has turned Mitt Romney from the sort of politician that would have agreed with Bloomberg, to one that has had to chase votes from the most fanatical, paranoid, xenophobic, anti-science, extreme factions of our society. It's Bloomberg's critique not just of Romney, but of the process that he was submitted to and the transformation he allowed to take place.

When Bloomberg feared having to pander to those voices, he left the Republican Party. When Romney wanted to become a presidential candidate, he capitulated to them. And that, more than anything, is the difference between the two.

Not everyone would care for a Bloomberg endorsement. Conservatives think he's too lefty. Liberals (myself included) have opposed him on extending term limits, suppressing Occupy Wall Street and his ceaseless defense of Wall Street's worst players. Bloomberg doesn't have a political base, which is why he never ran for national office, other than the pundit class that craves cross-partisan characters. If nothing else, though, winning over a few Thomas Friedmans and David Brookses to Obama is a useful measure.

What would be more useful is if this announcement signifies that Bloomberg not only endorses the candidate, but will push the president to govern in meaningful and ambitious ways over the next four years on the issues the Mayor cares most about: comprehensive immigration reform, marriage equality, illegal guns and, yes, climate change.

Even more meaningful - if the president's acceptance of Bloomberg's endorsement is his own endorsement of those ideas, and his commitment to governing for the next four years with the competence, compassion and commitment he has put on display this past week.