Newark Mayor Cory Booker announces his plans to run for the U.S. Senate seat that opened with the death of Frank Lautenberg (D-N.J.) during a news conference in Newark, N.J. on June 8, 2013. Booker, 44, is currently serving in his second term as mayor. At center is former Sen. Bill Bradley. (AP Photo/Rich Schultz) by Angela Delli Santi NEWARK, N.J. (AP) — Newark Mayor Cory Booker, who formally declared his candidacy for U.S. Senate on Saturday, now finds himself competing in a primary against like-minded Democratic congressmen that will be decided in mid-summer, when exceptionally low voter turnout threatens his early advantage.