Tumbler?

Barack the renegade, say secret service

The Democratic presidential candidate Barack Obama has been variously characterised as the bright young hope of the nation, a know-nothing upstart and a rebel without a cause. But for the wired-up, sunglassed, lapel-murmuring men and women of the US secret service, the senator from Illinois is known simply as "renegade", it was revealed yesterday.
(snip)

The ex-Hollywood cowboy Ronald Reagan was known to his secret watchers as "rawhide", George Bush Snr was "timberwolf", due possibly to his love of hunting. Jimmy Carter, a former Sunday school teacher, was the "deacon". The former vice-president Al Gore was "sawhorse".

Hillary Clinton, Mr Obama's rival for the party's nomination, is "evergreen". Her husband, Bill Clinton, is "eagle".

Most intriguingly of all, perhaps, the current president, George Bush, is known to the secret service as "tumbler".

I've heard "Rough Tumbler" used as slang for a street thug type man. Like an old fashioned gang member. Wonder which way they mean it?