Republican US Senator Scott Brown and his leading Democratic challenger, Elizabeth Warren, are tied in a new poll timed to gauge the impact of a controversy over Warren’s Native American heritage. The automated poll of 500 likely voters was taken Monday night by Rasmussen reports and shows both candidates at 45 percent. The same polling firm had similar results last month, with Brown leading 46 percent to 45 percent, with a margin of error of plus or minus 4.5 percent.