The governor of Massachusetts is spoiling for a fight. William Weld, the popular two-term Republican whom many GOP moderates considered presidential timber, announced that he'll challenge incumbent Democratic Senator John Kerry in next fall's elections. Why would the popular, just-reelected governor seek the change? "He's bored," says Boston bureau chief Sam Allis. "Weld accomplished much of what he set out to in his first term and is looking for bigger leagues. He'd be comfortable in Washington, and he's probably Newt Gingrich's favorite governor in the nation." At a press conference in Boston Wednesday, Weld took credit for balancing the Massachusetts budget and reforming welfare while portraying Kerry as a tax-and-spend liberal. "Now it's time to change the political culture of Washington, D.C.," he said. But defeating Kerry will be no picnic. "Though he lacks the passionate cadre of supporters that supports Ted Kennedy, Kerry has brought the bacon home effectively and is popular with the business community," says Allis. "Not only is he a tough campaigner, he's just married the heir to the Heinz food fortune. He's got the money."