PROVIDENCE, R.I. — With a voice hoarse not from last week’s Massachusetts Democratic convention, but from “the parties,” she said, Elizabeth Warren took the stage at the annual Netroots Nation conference here Friday afternoon with a clear goal: link her GOP opponent, Sen. Scott Brown, to the presumptive GOP nominee, Mitt Romney. The Harvard professor and Democratic Senate nominee made no mention in her 10-minute remarks of the months-long flap over her Native American heritage, an imbroglio that the Brown campaign as seized upon and that polls suggest could take a toll on Warren in November. Rather, Warren’s only allusion...