Rand Paul made his name as a gadfly preaching about the dangers of a tyrannical federal government. Now, after the killings of two Minnesota residents at the hands of Homeland Security agents, the Kentucky Republican has a chance to do something about it. The 63-year-old, who spent years on the outskirts of the party, is now at the center of the Senate’s response to the deaths of Renee Good and Alex Pretti, which have sparked new criticism of the administration’s immigration enforcement policies and raised many of the same civil liberties questions Paul has long been asking. As chair of...