"Why does McCain keep praising Gov. Tom Ridge?" asks the Atlantic's Marc Ambinder this afternoon. It would have been the last question conservatives wanted to ponder on the eve of McCain's expected VP roll-out if they weren't already gulping nervously about the very real possibility that a freaking Democrat could be second in line to their septuagenarian Republican president.

Despite his service with the Bush administration in the aftermath of the 9/11 attacks, Ridge is widely distrusted by the Republican voter base for a number of reasons. He's pro-abortion, against missile defense and, as we've noted before, possesses a massive jaw that can be unhinged to facilitate the consumption of large prey. The appeal of the former Vietnam veteran to McCain, however, is diverse: a close personal friendship, fewer houses than Mitt Romney, national security heft, and a possible huge boost to Republican prospects in the battleground state of Pennsylvania. Barack Obama currently leads McCain in Keystone State polls by around seven points, but Pennsylvania Governor Ed Rendell has surmised that a Ridge selection would immediately put McCain within striking distance of the Democrat.

Republican hard-liners can take heart from a National Review report that "the person to watch is [Minnesota Gov. Tim] Pawlenty," or rumors that Ridge was just taken off the schedule for a McCain event on Saturday if they want, but it's hardly safe to assume that McCain won't defy the Republican base. For his part, McCain is claiming he still hasn't made his choice, which seems unlikely given that his campaign will be trying to step all over Obama's convention bounce with an announcement by early tomorrow.