LONDON—A groundbreaking deal to curb Iran’s nuclear program faces towering obstacles at home and abroad to becoming a permanent agreement, starting with the U.S. Congress and two of America’s closest allies. The leaders of both the Democratic and Republican parties are threatening to break with President Barack Obama ‘s policy and enact new punitive sanctions on Iran, arguing that the interim deal reached in Geneva on Sunday yields too much to the Islamist regime while asking too little. “The disproportionality of this agreement makes it more likely that Democrats and Republicans will join together and pass additional sanctions when we return in December,” said Sen. Charles Schumer (D., N.Y.), an influential member of the Senate Democratic leadership. Such a move could kill the nascent nuclear accord, U.S. and Iranian officials agree, and add to more recent political embarrassments for the White House. Reaching a comprehensive deal with Iran also […]