The Lou Dobbs-for-Senate rumor had barely crested when the Lou Dobbs-for-president rumor suddenly overtook it this week. Mr. Dobbs, the former cable television anchor of the sonorous voice and tough-talking immigration politics, parted ways with CNN on Nov. 11, reportedly receiving an $8 million severance payment, and immediately stirred questions about his plans. His name was quickly floated as a potential challenger in 2012 to United States Senator Robert Menendez, the New Jersey Democrat, an ardent advocate for immigrants’ rights and the chamber’s only Hispanic member. (Mr. Dobbs, 64, lives on a horse farm in rural Wantage, N.J.) Then, on...