Caro sat down for an interview with The Huffington Post in conjunction with the release of the fourth volume of his biography, "The Passage of Power," which covers Johnson's vice presidency and some of his presidency.
"Harry Reid as a majority leader operated in near impossible circumstances," Caro said. "The other side is intractable and it has the votes to stop legislation. That he has been able to get as much as he has -- as little as it is -- through the Senate is a tribute to him as majority leader. I think he's in near-impossible circumstances. I think he's done a terrific job."