President Obama delivers the commencement address for the 2016 class of the U.S. Air Force Academy in Colorado Springs on June 2. (Pablo Martinez Monsivais/Associated Press)

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If you look at the polls, it is clear who’s winning the 2016 presidential contest: Barack Obama.

There remains the technical impediment that the president is constitutionally barred from a third term. But the longer the campaign goes on, the higher Obama’s approval rating rises. This should be bad for Donald Trump and good for the eventual Democratic nominee, almost certainly Hillary Clinton. But it is even better for Obama’s legacy.

According to Gallup, which has been charting the nation’s assessment of its presidents longer than anyone else, Obama’s approval stands at 52 percent, compared with 44 percent disapproval. That may not look impressive but it is actually quite good for a president nearing the end of his second term; Ronald Reagan, by comparison, had 49 percent approval at this point in his tenure.

For most of last year, Obama’s numbers were upside-down — more Americans disapproved than approved. So there are two obvious questions: What airport is going to be renamed Obama International? And why the turnaround?

I believe the increasingly warm feelings about the president must have something to do with the contrast between him and his potential successors. Trump and Clinton may be the most widely disliked major-party contenders ever (though Trump is arguably in a class of his own, with nearly two-thirds of Americans saying they would never, under any circumstances, vote for him as president.)

The speculation about when Trump will shift tactics and begin acting “presidential” is laughable. It should be clear by now that Trump is not only unwilling to change but incapable of doing so. Look at the way he continues to lash out at anyone he perceives as having slighted him — New Mexico Gov. Susana Martinez (R), for example, a potentially valuable ally whom Trump is determined to make into an enemy. Look at the news conference Tuesday at which he lashed out at a reporter, calling him a “sleaze,” for having questioned Trump’s record of charitable giving.

Then look at Obama. Whatever you think of his policies, not for a minute has he failed to comport himself with the dignity and gravitas required to serve as president. Never has he given the impression of acting out of pique rather than calculation. Never does he seem a threat to put ego-gratification above what he believes to be the best interests of the nation.

I’m setting a low bar here. The fact that Trump does not clear it has to engender a degree of fondness for Obama — and has to help Clinton, who does the gravitas thing just fine.

Another factor in Obama’s rising approval has to be the realization that despite Republican proclamations of doom and gloom, on balance things are going pretty well. Slow but steady economic expansion has not only reduced unemployment to 5 percent but also perhaps begun to move the needle slightly on incomes. Consumer confidence, an important indicator, is up. The effect of the recovery hardly feels like a boom but is nothing like the total bust that Trump and other Republicans describe.

The president has been increasingly forthright in showcasing his administration’s record — his remarks in Indiana on the economy this week sounded almost like a vintage Obama campaign speech. He has also demonstrated his intention to do everything he can to ensure that his successor is a Democrat who seeks to build on his achievements, not dismantle them.

Like many presidents in their final months, Obama is spending considerable time and effort on foreign affairs. Here, too, we see contrast and legacy. He has fundamentally changed the U.S.-Cuba relationship in ways that will be hard for anyone to reverse. He has continued to act with extreme caution in the Middle East, resisting calls for substantial deployment of U.S. combat forces. He made a bold statement against nuclear proliferation by visiting Hiroshima and hugging a survivor of the atomic bombing that turned the city into a smoldering wasteland — confronting the past without apology but with sober reflection.

Trump, on the other hand, believes it would be fine if Japan and South Korea got nuclear weapons of their own.

We tend to appreciate presidents more after they leave office. The inevitable reassessment of the Obama years seems to be starting early — perhaps in apprehension of the years to come. Even Obama’s harshest critics have to admit he was a steady hand in the White House. Reflection on this fact can only increase Clinton’s chances against a man who prides himself on being combative, capricious and cocksure.

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