WASHINGTON — President Obama, declaring himself on “the right side of history,” called on Congress on Monday to ban job discrimination against gay and lesbian Americans as he signed an executive order doing so for workers of federal contractors. In a ceremony at the White House, Mr. Obama noted that in much of the country, companies can fire employees based on their sexual orientation. “That’s wrong,” he said to an audience of supporters. “We’re here to do what we can to make it right — to bend that arc of justice just a little bit in a better direction.” President...