Sen. Scott Brown (R-MA) has turned out to be the moderate, relatively independent Republican he said he would be. In other words he turned out not to be what many of his supporters hoped or imagined he would be.

When Brown beat Martha Coakley to win Ted Kennedy's old seat in January, he became a conservative hero. He had won an improbable victory against an overconfident Democratic machine in a solidly blue state. It was an enormous symbolic victory for Republicans, and seemed to be the turning of the tide that had swept them out of office a year before. Brown's election meant the end of the Democrats 60-vote majority in the Senate and would—it seemed—kill the Democrats' chance of passing health care reform.

But Brown's election didn't prove to be the turning point conservatives hoped. The Democrats' supposedly filibuster-proof majority was, as Mark Schmitt argues, always an illusion. The Democrats managed to pass health care reform without it in any case. And although the Democrats probably will lose a substantial number of seats in Congress, the fall elections no longer look like quite the rout they seemed they would be. Brown himself, while certainly no Democrat, has not been the stalwart conservative some of his supporters had hoped he would be.

In his first vote as senator, Brown was one of just five Republicans to join with Democrats to pass a $15 billion jobs bill. He  crossed party lines on the financial reform bill strongly opposed by the Republican leadership too. "Listen, I have always said I don’t work for Mitch McConnell and I don’t work for Harry Reid, I work for the people of Massachusetts," Brown told The New York Times. "I am not quite sure what all the surprise is, and people wondering kind of like, 'wow, he’s independent.' I have always been this way."

It shouldn't be a surprise. Massachusetts is still a liberal state, after all. And while Brown did court the support of national conservatives, he has never been all that conservative himself. As Boris Schor predicted when Brown was elected, Brown has turned out to be—alongside Sen. Olympia Snowe (R-ME) and Sen. Susan Collins (R-ME)—one of the most liberal Republicans in Congress.

When Brown was elected, I wrote that he had a choice. He could move to the right and use his celebrity to become a Republican figure on the national stage. He might even try to make a run at the presidency at 2012. But that would be a longshot, and moving to the right would almost certainly doom his chances of being reelected to the Senate when his term expires two years from now.

Or Brown could stay in the center the way he so far has. He will inevitably be accused of being a RINO—a Republican in Name Only—and draw fire from his old Tea Party supporters. But the Republican leadership will for the most part understand. They know a Republican from Massachusetts can't vote the same way a Republican from Kentucky can and still hope to get reeelected. They know staying in the center is likely Brown's only chance of a having a political future in Massachusetts.