This assessment, from Garance Franke-Ruta over in The Atlantic, probably has some truth to it:
I said it after the convention speech and I’ll say it again: If there’s something that seems shut down in our once ebulliently optimistic president, it most likely has to do with the wars. Obama is a naturally empathic individual, whose diverse, mobile, international background made him unusually able when it came to assessing new social situations and reading more than people say. Some observers have speculated that Obama needs a crowd, energy he can draw from. But he had that aplenty in Charlotte, and it barely helped. I suspect a more prosaic explanation: A person of his temperament cannot maintain the same open demeanor when he’s dealing with war and death all the time. As, we must recall, Obama has been for years now. If Obama seems shut down, perhaps it is because he has to be to be who he is and do the job he needs to do day in and day out. If his heart didn’t seem in it last night, I wonder if it’s not in part because the last thing he needs to consider in his work on a day-to-day basis is his heart. It’s a long way from being a community organizer, civil-rights lawyer and anti-war state senator to running a drone war that kills innocent civilians, ordering the death of militants, overseeing a policy that’s led to an increase in American casualties in Afghanistan, and delivering funereal remarks at a ceremony honoring the returning remains of a slain American diplomat.
We often hear about the Oval Office rapidly aging its occupants; undoubtedly the stress and responsibility of dealing with life-and-death issues, day after day, accounts for some of that toll.
But it also may be that Obama entered the presidency with a visage and psychology that would be particularly challenged by that toll. Youth and vigor and an optimistic “hope and change” attitude are inevitably going to be worn down by four years of security briefings about efforts to kill Americans, reports of casualties of war, disappointing policy results, and anti-Americanism that is proving resilient and immune to any public diplomacy effort.
Thinking back to Jodi Kantor’s The Obamas, pp. 313–314:
“When you ran for president, you awakened something in this country I haven’t seen since President Kennedy,” [Obama donor Judee von Seldeneck] said, looking directly at the president. “Why don’t you provide the leadership we all expected from you and desperately need?” It was the elephant in the room: what had happened to the Barack Obama of 2008?
The other donors applauded.
His answer was weak, von Seldeneck said later. Looking irritated, the president used a line he deployed a lot that summer, about being wiser, grayer, battle-tested. He blamed some of his ills on Congress, and said he needed to see the upcoming debt ceiling negotiations through. “I can’t come untethered yet,” he said, and von Seldeneck wondered what that meant.
He acknowledged the way his former success hung around his neck.“I’m running against the Barack Obama of 2008,” he said, but he also made what sounded like an unrealistic promise. “If you thought the last campaign was something, you just wait for the next one. It’s going to be better,” he finished.
You can’t expect any incumbent president to emulate the optimism, the excitement, the energy, and the good cheer of the Barack Obama of 2008. Because the Barack Obama of 2008 didn’t know what he was in for.