WASHINGTON -- Harry Reid, as majority leader of the United States Senate, has done "a terrific job," according to the most celebrated historian of the institution in a generation. Robert Caro, author of "Master of the Senate," the Pulitzer Prize-winning volume of his Lyndon Johnson biography, said that Reid's opponents and their abuse of the filibuster have made running the upper chamber "near impossible."

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."

In Johnson's time, only 34 votes were needed to sustain a filibuster. Today, as a result of filibuster reform a generation ago, 60 votes are needed to break a filibuster and invoke what's known in the Senate as cloture. While the reform increased the number of votes the minority needed to hold to sustain the filibuster, it flipped the onus around: Pre-reform filibusters could be broken by a vote of two-thirds of those present, putting the onus on the minority to keep their troops on the floor. Today, a full 60 votes is needed to invoke cloture, as long as at least one of the opposing senators is on the floor.

Should the Senate rules be changed as a result of GOP intransigence?

"That's such a hard question, because we will want it if the tide turns against us," Caro said. "The right of a minority is so important in a democracy. And in the Senate, the right of unlimited debate is the protection of the right of the minority. It's really a hard question to answer because at the present time, it's being used in an unconscionable way. But to say it should be substantially weakened because it's being used in a bad way isn't the answer either."

But, he said, he doesn't have a firm position on it. "I'm conflicted about it, but if you read Madison ... saying you've got to have something against the right of the majority, otherwise it's just the rule of the mob, I mean, you say, 'Boy, that's a basic truth, you know.' So he convinced me at the time. But to see how they've used it..."