WASHINGTON -- Senate Democrats, their party's last line of defense against GOP hegemony in Washington, are coming off their best week since handing over control of their chamber to Republicans three years ago. Republicans outnumber Democrats in the upper house by a solid 55-to-45 margin, but seldom have those numbers seemed less meaningful than in the recent weeks, when Democrats have frustrated, derailed and detonated key elements of the GOP legislative agenda. "The Democrats are starting to draw blood and cause some pain for the Republicans," said Jennifer Duffy, who monitors the Senate for the nonpartisan Cook Political Report. "They...