(Photo by Charles Dharapak/AP)

You can’t really dispute Lawrence Summers’s suggestion on Monday that second terms, including President Obama’s, often seem “ineffectual.” George W. Bush’s Katrina and the financial crisis, Bill Clinton’s impeachment, Ronald Reagan’s Iran-Contra, Richard Nixon’s resignation, Lyndon Johnson’s Vietnam War: The list goes on. Perhaps surprisingly for a renowned economist, Summers draws causality out of this correlation. He suggests that presidents should be limited to one term, perhaps six years long.

It’s quite something for Summers to say this. He was Obama’s top economic adviser for two years, in the beginning of the first term, and continues to consult the president. He served all of Clinton’s administration, finishing up as Treasury secretary. Clinton alumni usually want to be remembered for the technology boom and amazing economy of the mid- to late-1990s, but Summers writes that his former boss’s “second term will be remembered for scandal and his impeachment by the House.”

Summers has a little to say about  why this “stunning American political regularity” occurs. He suggests that as presidents seek reelection, political conditions polarize, making second-term legislative achievements all the more unlikely. He also suggests exhaustion and political paralysis might just compound over the course of a president’s two terms, making bipartisanship harder to achieve in the final four years.

I find these arguments unpersuasive -- but the question of why second terms are routinely so challenging remains interesting.

For starters, it should be noted that while so many second terms are remembered as disastrous, it's not quite true to say they are achievement-free. Obama has put in motion historic rules to limit greenhouse gas emissions by power plants. Bush committed himself to saving the financial system in the final months of his term. Reagan oversaw a big rewrite of the tax code and an important new arms treaty with the Soviet Union.

But second terms inevitably fall far short of expectations.

Let’s look at Obama’s record. It’s not quite fair to say his second term has been ineffectual. It would be more accurate to say that, in terms of legislative accomplishment, most of his presidency has been ineffectual. He accomplished a tremendous amount in 2009 and 2010 when his party controlled Congress. Since Republicans took control of the House in January 2011, however, Obama has had virtually no legislative achievements. He's tried negotiating, he tried pressuring, and nothing has worked. The 2012 election — a resplendent endorsement of his views — hasn't changed anything.

Similarly, it's hard to say that Bush’s inadequate response to a historic hurricane, or Clinton’s decision to have sexual relations with an intern, was the result of a second-term regularity. These were the results of decisions that specific presidents made -- in dissimilar contexts.

An economist might suggest that, perhaps more than the existence of a second term, the impossibility of a third term is what causes a president to fail so often in the final four years. Reelection is an amazing incentive. In a second term, a president is fighting for legacy, for the good of the party, but neither is arguably as compelling an incentive as one’s own reelection. There’s a reason that the president’s party is often rejected in mid-terms, and a two-term president is often replaced by a new president of the opposing party. By contrast, two-term presidents have -- obviously -- won election twice.

Perhaps it’s the case that if Bush were going to face reelection, he would have acted more decisively to help the victims of Katrina. Hard to know, but I would guess that Clinton might have behaved a little more honorably, and intelligently, if he knew he had a chance for a third term. It's probably healthy for society to limit how long a person holds the nation's highest office -- the sight of a possible Clinton-Bush presidential race notwithstanding -- but whether it actually has more benefits than costs is an open question.

UPDATE: Some have rightly pointed out that Clinton began his relationship with Monica Lewinsky in his first term. Indeed, many second-term disasters have their roots in the first term, including Watergate and Iran-Contra, as this article points out. I still think there's a case to make that Clinton had questionable personal conduct throughout his life, but didn't commit the alleged offenses leading to his impeachment -- perjury and obstruction of justice -- until his second term. The particulars aside, there still might be a powerful incentive missing in a president's second term that makes them underperform. Or it might be something else entirely. Or nothing at all.