This week’s endorsement of Florida Gov. Charlie Crist by senior Senate Republicans is being cheered by GOP senators as a move toward the middle. Minority Leader Mitch McConnell (Ky.) and National Republican Senatorial Committee Chairman John Cornyn (Texas) endorsed Crist over former state House Speaker Marco Rubio, a protégé of former Gov. Jeb Bush and a more conservative candidate. The decision by McConnell and Cornyn was the first such choice since last month’s defection of Arlen Specter to the Senate’s Democratic conference. Moderate GOP senators like Susan Collins and Olympia Snowe of Maine used that opportunity to publicly warn the...