In an interview in January 2010, President Obama told Diane Sawyer of ABC News, “I’d rather be a really good one-term president than a mediocre two-term president.”

The comment didn’t really jibe well with Robert W. Merry, an acclaimed biographer of James Polk, who served as president from 1845 to 1849. Polk is ranked as a “near great” president in polls by scholars, but he is an exception. “History has not smiled upon one-term presidents,” wrote Merry in an editorial in the New York Times. “The typical one-term president generally falls into the ‘average’ category, occasionally the ‘above average.’ ”

In his new book, Where They Stand, Merry opens up the rating game beyond historians, to include what voters and contemporaries said in their own times. The editor of the National Interest, a foreign policy publication, argues that while historians’ views are important, presidential greatness is best seen through the eyes of voters of the president’s time. The greatest of the “greats,” in other words, have the election records to show it. They earned the trust of Americans in their first terms, won second terms and, in some cases, paved the way for their party to maintain control of the White House for the next four years.

Historians and others take joy in ranking the presidents, and debating these ranks. To you, what’s the fun in this?
It is the same fun that we have in trying to determine who is the greatest first baseman of all time. Most people would say Lou Gehrig, but there is plenty of room for debate. Who is the greatest American singer of the postwar period? But the presidents really have the national destiny in their hands. It is a much more significant pursuit than these others, which are more in the realm of trivia. Who was great? Who wasn’t so great? And, why were they great? Ranking presidents is a way we bring order to our thinking about our history.

What factors, do you think, need to be considered when assessing presidential greatness?
Greatness is as greatness does. It is really a question of what a president has accomplished with the country. Reagan’s question, “Are you better off than you were four years ago?” is very apt. Put another way, is the country better off? How is the country different? Are those differences good or are they not so good?

The great presidents all did something that changed the political landscape of America and set the country on a new course. That’s not easy to do. That is really the key to presidential greatness.

In your book, your big claim is that we should listen to the electorate at the time of the president’s term, and not just historians. Why do you put such emphasis on the voters?
Presidential politics is like retailing. The customer is always right. In our system, we put faith in the voters, because that is at the bedrock of how we think we should order our affairs politically. If you don’t believe that, then it is kind of hard to believe very strongly in American democracy.

The whole idea is that the voters emerge with a collective judgment, maybe even occasionally a collective wisdom. I happen to buy that. Therefore, I felt that the polls of historians were significant. I didn’t debunk them or toss them aside. But I thought they were incomplete, because they didn’t always take into account what the voters were saying, thinking or doing with regard to their presidents contemporaneously. I wanted to sort of crank that into the discussion.

There are six presidents that you refer to as “Leaders of Destiny.” What makes a president deserving of this title?
The six, in order, are Washington, Jefferson, Jackson, Lincoln, Teddy Roosevelt and Franklin Roosevelt. I happen to believe that Reagan will get into that circle, but right now, the polls of historians don’t quite have him there, although his standing is rising rather dramatically.

The six leaders of destiny pass a three-part test. They are consistently hailed among the greats or near greats by the historians. They are two-term presidents succeeded by their own party, meaning that the voters liked them both times that they served. And then, as I described earlier, they transformed the political landscape of the country and set it on a new course.

What were the major traits that these presidents shared? They all understood the nature of their time, what was really going on in the country, what the country needed, what the voters collectively were hungry for. There are a lot of presidents who don’t understand their time; they think they do, but they don’t. You have to have a vision. All of these leaders of destiny were elected at a time when the country needed tremendous leadership, and these presidents are the ones who stepped up and gave it. Then, they have political adroitness, the ability to get their hands on the levers of power in America and manipulate those levers in a way that gets the country moving affectively in the direction of that vision.

In your opinion, FDR and Ronald Reagan are the two greatest presidents of the 20th century.
The voters hailed them both at the time. What is interesting, in my view, is that Roosevelt was probably the most liberal president of the 20th century, and Reagan was probably the most conservative president of the 20th century. It indicates that the country is not particularly ideological. It is looking for the right solutions to the problems of the moment. The country is willing to turn left or to turn right.

What is the difference between good and great?
We have had a lot of good presidents. I’ll give you a good example of a good president, Bill Clinton. Clinton was elected because the country wasn’t quite satisfied with George H.W. Bush. They didn’t think he was a terrible president, but he didn’t quite lead the country in a way that made him eligible for rehire. The country gets Bill Clinton, and he tries to govern in his first two years as if his aim is to repeal Reaganism. The result was that the American people basically slapped him down very, very decisively in the midterm elections of 1994, at which point Bill Clinton did an about-face and said, “The era of big government is over.” He crafted a center left mode of governing that was very effective. He had significant economic growth. He wiped out the deficit. We didn’t have major problems overseas. There was no agitation in the streets that led to violence or anything of that nature. He gets credit for being a good president.

Once he righted his mode of government and moved the country solidly forward, he was beginning to build up some significant political capital, and he never really felt the need or desire to invest that capital into anything very bold. So, he governed effectively as a status quo president and ended eight years as a very good steward of American polity, but not a great president. To be a great president, you have to take risks and make changes.

Just as we can learn from the successes, there are lessons to be learned from the failures. What can you say about character traits that do not bode well for a successful presidency?
Scandal harms you tremendously. But I would say that the real failures are people like James Buchanan who faced a huge crisis—the debate over slavery that was descending upon America—and just simply didn’t want to deal with. He wasn’t willing to put himself out in any kind of politically risky way in order to address it. The result was it just got worse. It festered and got worse.

Occasionally, a president will make a comeback in historians’ minds. What would you say is the most reputation-altering presidential biography?
Grover Cleveland is the only president we have who actually is a two-time, one-term president. He is the only president who served two nonconsecutive terms. Each time he served four years, the voters said, “I’ve had enough. I’m going to turn away to either another person in the party or another candidate.”

Meanwhile, however, the first poll by Arthur Schlesinger Sr. in 1948 had Grover Cleveland at Number 8. That ranking came a few years after the great historian Allan Evans wrote a two volume biography of Grover Cleveland, in which he hailed him as a man of destiny and a man of character. I am sure that biography had a significant impact.

So, you describe a manner of assessing the greatest of past presidents. But, it is an election year. How do you suggest we evaluate current presidential candidates?
I don’t think the American people need a lot of instruction from me or anyone else in terms of how to make an assessment on the presidents when they come up for reelection. Presidential elections are largely referendums on the incumbent. The American people don’t pay a lot of attention to the challenger. They basically make their judgment collectively, based on the performance of the incumbent or the incumbent party. They pretty much screen out the trivia and the nonsense—a lot of the stuff that we in the political journalistic fraternity (and I’ve been a part of it for a long, long time) tend to take very seriously—and make their assessment based on sound judgments on how the president has fared, how well he has led the country and whether the country is in better shape than it was before. I am pretty confident that the American people know what they are doing.

Do you have any comment, then, on what qualities we might look for in a candidate, so that we maximize our chances of electing a leader of destiny?
One thing that we know from history is that the great presidents are never predicted as being great. They are elected in a political crucible. While supporters are convinced he is going to be great—or she; someday we will have a woman—his detractors and opponents will be absolutely convinced that he is going to be a total and utter disaster. Even after he is succeeding, they are going to say he is a disaster.

You can never really predict what a president is going to do or how effective he is going to be. Lincoln was considered a total country bumpkin from out there in rural Illinois. Oliver Wendell Holmes famously judged Franklin Roosevelt as having a first-rate temperament and a second-rate intellect. Ronald Reagan was viewed as a failed movie actor who just read his lines from 3-by-5 cards. And all three were great presidents.

What idea are you turning to next?
I wrote a history of the James Polk presidency [A Country of Vast Designs] and how the country moved west and gained all of that western and southwestern territory, Washington, Oregon, Idaho and then California to Texas. I am fascinated now by the subsequent time in our history when we busted out of our continental confines and went out into the world in the Spanish-American War. I am looking at the presidency of William McKinley and the frothy optimism of the country at that time when we decided to become something of an imperial power.

This interview series focuses on big thinkers. Without knowing whom I will interview next, only that he or she will be a big thinker in their field, what question do you have for my next interview subject?
I guess a big question I would have in terms of the state of the country is, why is the country in such a deadlock? And how in the world are we going to get out of the crisis that is a result of that deadlock?

From my last interviewee, Frank Partnoy, a University of San Diego professor and author of Wait: The Art and Science of Delay: How do you know what you know? What is it about your research and experience and background that leads you to a degree of certainty about your views? With what degree of confidence do you hold that idea?
I am not a young man. I have been around a long time. I had certainty when I was young, but I have had a lot of my certitudes shaken over the years. But, if you have enough of that, you tend to accumulate at least a few observations about the world that seem pretty solid and grounded. So, you go with them.

You have to take it on faith that you have seen enough and you know enough and you have certain principal perceptions of how things work and how events unfold and how the thesis-antithesis leads to synthesis in politics or government or history. And, so you pull it together as best you can. Ultimately, the critics will determine how successful you were.