In his bid for reelection, US Senator Scott Brown is calling for tighter immigration policy and chiding his leading Democratic challenger, Elizabeth Warren, for her seeming opposition to the federal enforcement program known as Secure Communities. But Warren refuses to be pinned down on the heated issue, calling for a more nuanced debate. Though in the past, she has appeared to oppose the initiative, Warren last week would not declare a position, instead calling for further discussion with police about how the program has been working in other states.