Democrats now control Congress. What should they do first?

President Joe Biden enters office with one of the most ambitious policy agendas of any modern president. He can accomplish many of these goals through executive orders, but his most transformative proposals — on everything from health care to climate change to education — will need to be approved by Congress.

Fortunately for Biden, Democrats hold majorities in both the House of Representatives and the Senate. But recent history shows that unified control doesn’t mean Congress will swiftly rubber-stamp everything on the president’s to-do list.

Democrats had strong majorities in...