I'm not American, so your politics are largely irrelevant to me, but as an American I would find it probably worth looking at Obama's stance on bulk surveillance over time. Has he flip-flopped?
If so, either he was persuaded by evidence of its effectiveness in preventing terrorist attacks on the US, or maybe he was persuaded by evidence of its effectiveness after being shown his last 10 years of internet searches, presented on a CD, lying next to the duplicate sitting in an envelope marked "To the Editor, New York Times".
He doesn't want a serious attack to happen on his watch. There's a strong incentive to do "everything possible" to prevent one. Very few people would reward him for reigning in his own power, but nearly everyone will blame if an attack happens.
If so, either he was persuaded by evidence of its effectiveness in preventing terrorist attacks on the US, or maybe he was persuaded by evidence of its effectiveness after being shown his last 10 years of internet searches, presented on a CD, lying next to the duplicate sitting in an envelope marked "To the Editor, New York Times".