Four days after the Democratic debate in Charleston, S.C., more than 400 questions directed to the GOP presidential field have been uploaded on YouTube, as Republicans are scheduled to take their turn at video-populism on Sept. 17. But only Sen. John McCain (Ariz.) and Rep. Ron Paul (Tex.) have agreed to participate in the debate, co-hosted by the Republican Party of Florida in St. Petersburg. "Aside from those two candidates, we haven't heard from anyone else," said Sam Feist of CNN, which is co-sponsoring the debate with the popular video-sharing site. Rudolph W. Giuliani and Mitt Romney, both with dozens...