Every president, indeed every politician, is to some extent both creature and captive of his political base. If you stray too far from it to win over other voters, you risk losing your strongest backers: Those who give the most money and defend you the most, who knock on doors for you and turn out the vote on Election Day.

You may not be able to win an election just with your base, but you almost certainly can't win without it. That may help explain why President Obama has decided to go to Copenhagen later than originally planned in the hope he can be part of a political agreement on climate change this week.

An "agreement" would fall well short of the binding treaty climate change activists had hoped for and it won't help him much with the broader American public which is far more worried about the U.S. economy than any climate deal which would further burden that economy.

But remember: President Obama bucked his base on a major issue just last week when he decided to send more troops to Afghanistan, a war the left opposes.

So despite the low priority Americans now assign to climate change and despite the scandal swirling around those leaked e-mails that cast serious doubt on the integrity of leading climate scientists, the president is raising the stakes by going in at the end.

It may not achieve much on climate change and it certainly won't help the economy, but there's political logic to it anyway.

Brit Hume is the senior political analyst for Fox News Channel.