Opposition leader Juan Guaidó staged a dramatic return to Venezuela on Monday despite government threats to arrest him, energizing the country’s opposition and raising the stakes in the political showdown with President Nicolás Maduro’s government. Having flouted a government travel ban by leaving the country more than a week earlier, Mr. Guaidó arrived at the Caracas airport on a commercial flight from Panama and calmly walked through immigration, emerging to deafening cheers from hundreds of supporters…