BIRMINGHAM, Ala. — Republican voters here put a bitter Senate campaign into overtime, forcing Sen. Luther Strange (R-Ala.) into a runoff with conservative jurist Roy Moore for the right to represent Attorney General Jeff Sessions’s old seat. Strange was endorsed by President Trump, the National Rifle Association and Senate Majority Leader Mitch McConnell’s super PAC, which spent $2.5 million on TV ads to boost him in Tuesday’s primary. That helped push him past Rep. Mo Brooks (R-Ala.), saving national Republicans from an embarrassment in a unique mid-summer election marked by low turnout. Democrats, who have not won a Senate race...