The 2013 decline is not surprising. Obama's approval rating was on the rise through 2012 and the beginning of 2013 -- when he was fresh off a reelection victory. But since that time, he's dealt with revelations about sweeping government surveillance, tried to convince a war-weary public and Congress to take military action in Syria, and engaged in a lengthy fiscal debate involving a government shutdown. That's not exactly smooth sailing.
What it means is that dating back to the middle of the 20th century, Obama's 19th quarter in office is most comparable to Bush's and Truman's; their approval ratings were 43.9 percent and 45 percent, respectively.
It's far too early to draw any definitive judgments about how Obama's second term will be viewed by the public. As the months and years go on, here's one thing worth keeping in mind: Presidents have by and large been less popular in their second terms than their first.