If you go play around with Gallup's interactive presidential polling tool (which all good political obsessives should do with some regularity), you'll notice something: Since the end of his first year, and with the exception of a spike around the 2012 elections, President Obama's approval rating has been unusually steady.
If you look at the distribution of the most common approval ratings for presidents since Nixon (skipping Ford), you get a pattern that looks like this. The darker the bar, the more common that particular approval rating.
You'll notice that the overall range of approvals for Obama has fallen in a fairly tight range -- comparable to Presidents Reagan and Clinton. But that's the total range. The most common approvals Obama has seen have been within a relatively narrow zone in the mid-40s. (There are a lot more data points for Obama, we'll note, so his distribution is smoother as a result.)
By comparison, George W. Bush's approval was all over the place, with few dark-red bands because his approval was so broadly distributed. Even the more-popular Clinton saw a broader range of enthusiasm over his eight years.
One key reason for Obama's narrow fluctuations is that a large part of the population made up its mind early and hasn't wavered much: Republicans. By the end of his first year, Obama's approval among Republicans had fallen to 16 percent; it's rarely been above that since, settling into a general 7-15-point range. The fluctuations, then, have mostly been the result of Democrats embracing or ignoring the president -- and independents getting more or less enthusiastic.
Go back to that Gallup tool, and click "Historical Trend." Mouse over the parties and see how approval from Democrats and Republicans usually move up or down in tandem, albeit on opposite sides of the overall trend. Then notice that Democrats have been much more volatile in their opinion of Obama relative to their political opponents.
So what does it all mean? It means Obama will likely end up as one of the steadiest recent presidents when it comes to his polling numbers -- thanks largely to the steady opposition he's faced.