A Republican state senator who once posed naked in Cosmopolitan magazine last night won the contested Senate seat in Massachusetts. The upset — and for once, the word “stunning” really applies here — stripped the Democrats of their 60-seat caucus and throws up in the air a number of Democratic priorities including health care reform and a cap-and-trade system to regulate greenhouse gas emissions.

Sixty is a magic number in the Senate because it constitutes a ‘supermajority’ that can overcome procedural hurdles that otherwise mean one party can essentially block major legislation. After Ted Kennedy died last year, Massachusetts legislators conveniently reshuffled their laws to permit a Democrat to occupy the seat — and cast the crucial 60th vote — until a special election could be held. That election, held yesterday, saw Democratic candidate Martha Coakley, the state’s attorney general, lose to Scott Brown (pictured right).

Over at ClimateWire, Darren Samuelsohn reports on the ensuing confusion surrounding climate legislation. “A Brown win adds further bricks to the backpack of trying to bring climate change to the floor this year,” one source told him. The House of Representatives passed a climate bill last year, and the Senate was expected to take up its own version this spring. Adding to the confusion are rumours that Alaska senator Lisa Murkowski, citing costs, will soon introduce an amendment that would strip the Environmental Protection Agency of its ability to regulate carbon dioxide as a pollutant. When this might happen — as with all things Senate-related at the moment — is up in the air.

In the near term, the bigger impact will be not on climate legislation but health care reform. Even before the Massachusetts election the Democrats had not gathered 60 votes for a cap-and-trade bill (for a gorey breakdown of the voting likelihood of each senator, see Darren’s analysis here). Through a combination of last-minute wrangling and blatant vote-buying, however, the Democrats had managed to cobble together 60 votes for health care reform.

One thing’s for certain: the eternally grand and insufferably political stage that is the US Senate will continue to amaze, dumbfound, and annoy nearly all Americans.