San Francisco voters Tuesday will weigh in on the national debate over gun control by deciding whether to make their city home to the toughest handgun ban in the country. And in a place known for its left-leaning politics, gun opponents would seem almost guaranteed a victory. Proposition H would make it illegal for city residents to possess handguns, and those who already own them would be required to turn the weapons in to police by April 1. The measure also would make it illegal to buy, sell, distribute and manufacture firearms and ammunition within city limits, though there is...