(Reuters) - While President Barack Obama and top aides have been united this week in grave warnings over an alleged Iranian assassination plot, some U.S. government officials are privately expressing disquiet that the outlandish-sounding plan has triggered U.S. calls for stiff new action against Iran. These officials, while not disputing many facts of the case, say that if anything, the scheme reveals weaknesses in Iran's security agencies, and the increasingly fractured state of Iran's government as it faces intense international pressure. They also questioned the wisdom of the White House strategy in using the affair to rapidly push for tougher...