British Prime Minister Tony Blair just cast the vote that counts on President Bush’s “surge” plan in Iraq. Blair is pulling nearly 23 percent of British forces out of Iraq.

This is no mere rhetorical vote of no confidence. Unlike members of the U.S. House, Blair didn’t just “disapprove” of U.S. Iraq strategy.

He is showing he doesn’t like it by walking away.

Blair pretends the divergence in U.S. and British positions is just an anomaly of geography: Baghdad is dangerous. Basra is not.

British troops can leave because they are in relatively safe, Shiite Basra, while U.S. troops are stuck up north in dicey, multiethnic Baghdad.

Of course, Blair could have sent his 1,600 crack British troops north to support the U.S. security push. Instead, they’re leaving for good.

The remaining 5,500 British forces are to retire to out-of-the-way bases. Hundreds more will exit in coming months if Basra, Iraq’s second-largest city, stays quiet.

And Basra is likely to stay quiet. Its conflicts are among warlords and tribes, not sectarian factions.

Once the British forces are gone, Shiites in southern Iraq can turn their attention to what really matters: preparing for the coming war with Iraqi Sunnis.

Within Iraq, it’s all about positioning for an expanded civil war.

That’s why U.S. military planners should be focused less on the “surge” and more on how to avoid feeding additional arms and tactical advantages to factions blatantly readying for the next bloody phase.

U.S. officials want to spin the British departure.

“It is actually an affirmation that there are parts of Iraq where things are going pretty well,” Vice President Dick Cheney told ABC News Wednesday.

In a speech earlier in the day, Cheney argued the only way the “terrorists” win in Iraq “is if we lose our nerve and abandon our mission.”

But terrorism isn’t the main threat in Iraq.

Sectarian strife is the prism through which Iraqi life, politics – and war – all operate.

Iraq’s Shiite prime minister, Nouri al-Maliki, may be considered a moderate, but he’s tying cooperation in the U.S. “surge” to more training and weaponry for his mostly Shiite security forces. The radical Mahdi militants he was supposed to deliver to coalition forces are largely in hiding.

This week, a young Sunni woman shocked Iraqis by going on Al-Jazeera television to accuse three Shiite policemen of raping her after her arrest. It was an exceptional confession in a culture that usually blames the victim.

Yet instead of moving to calm the sectarian anger, al-Maliki aggravated it by publicly calling her a liar, praising the police allegedly involved and firing the prominent Sunni official who called for an investigation.

Of course, the woman, an alleged insurgent sympathizer, could have been lying. In the Iraqi sectarian pressure cooker, a rape allegation is its own form of political dynamite.

Yet the incident underscores again the need to do more planning to mitigate the potentially widespread bloodshed and regional warfare that would result from an Iraqi implosion. A premature British withdrawal in southern Iraq, for instance, could lift restraints that might be keeping radical Shiite militias there from arming against all Sunnis in Iraq.

Blair admittedly wants the troops home for more than just strategic reasons.

He’s facing his last months in office saddled with an Iraq engagement that has divided his party, sapped his popularity and alienated much of the public.

Yet these are the politics of a war gone bad, with a strategy that doesn’t make sense. It’s time to face up to the primary danger in Iraq: militant Iraqis’ seemingly undiminished appetite for killing one another.