WASHINGTON — When William Barr was attorney general in the early 1990s, he was outspoken about some of America’s biggest problems — violent crime, drug addiction, teenage pregnancy. The “Age of Aquarius,” he warned, had given way to crack babies and broken families, misery and squalor. The rhetoric reflected Barr’s deep-seated personal beliefs and was typical talk for a conservative Republican at a time when family values and tough-on-crime stances defined the party. Now, as President Donald Trump’s nominee for attorney general, Barr is poised to return to the same job in a dramatically different Washington. Republicans just pushed through the biggest criminal justice overhaul in a generation, easing prison sentences.