Past presidents have treated unified government — that is, one-party control of the White House and Congress — as an opportunity to enact bold legislative agendas. Franklin Roosevelt’s New Deal  reshaped banking protections and labor law and started Social Security. Lyndon Johnson’s Great Society  featured Medicare, Medicaid, civil rights and voting rights bills, as well as education reform. Barack Obama induced Congress to pass the Affordable Care Act, financial reform, and an $800 billion economic stimulus package.  But the 119th Congress, rather than using control of Washington to legislate, has voluntarily surrendered power to a president eager to take it.…