Democratic candidate for U.S. Senate Elizabeth Warren , left, faces reporters during a campaign stop at a diner in Shrewsbury, Mass., Sunday, April 29, 2012, as U.S. Rep. Jim McGovern, D-Mass., right, looks on. Warren and her opponent Republican U.S. Sen. Scott Brown have vowed to fight attack ads on television, radio and the Internet, but in their emailed appeals to supporters, the two routinely portray each other in the harshest light possible. (AP Photo/Steven Senne)

Democratic candidate for U.S. Senate Elizabeth Warren , center, greets Bruce Trotto, of Shrewsbury, Mass., right, owner of Dinky's Blue Belle Diner, during a campaign stop at the diner in Shrewsbury, Sunday, April 29, 2012, as U.S. Rep. Jim McGovern, D-Mass., left, looks on. Warren and her opponent Republican U.S. Sen. Scott Brown have vowed to fight attack ads on television, radio and the Internet, but in their emailed appeals to supporters, the two routinely portray each other in the harshest light possible. (AP Photo/Steven Senne)

Democratic candidate for U.S. Senate Elizabeth Warren , center, greets people at Dinky's Blue Belle Diner in Shrewsbury, Mass., Sunday, April 29, 2012. Warren and her opponent Republican U.S. Sen. Scott Brown have vowed to fight attack ads on television, radio and the Internet, but in their emailed appeals to supporters, the two routinely portray each other in the harshest light possible. (AP Photo/Steven Senne)