The Senate will begin consideration of Robert Groves nomination to lead the Census Bureau on Monday, after Majority Leader Harry Reid (D-Nev.) filed a procedural motion Thursday to break GOP-led opposition.The nomination of Groves, director of the University of Michigans Survey Research Center and a former Census Bureau official, has lagged for close to two months. The Homeland Security and Governmental Affairs Committee unanimously approved his nomination May 20.But Republican Sens. Richard Shelby (Ala.) and David Vitter (La.) had put holds on Groves nomination over concerns that he would use statistical sampling for the 2010 effort. Republicans charge that the technique, designed to better capture undercounted groups such as minorities, is unconstitutional and a political maneuver.