This is really one of those picture-says-a-thousand-words things. We took all of the available Gallup approval polling for each president since Harry Truman and figured out how often the president enjoyed each possible percentage of support. Maybe five polls had him at 50 percent and two had him at 30. That sort of thing. Then we plotted it from 0 percent support (which has never happened) to 100 percent support (same) to see how it was distributed.

But again: The pictures tell the story. What are you looking for? The extent to which President Obama's approval rating has moved in a stunningly small range over the course of his two terms.

George W. Bush saw huge swings, from his 9/11 popularity to his second-term, Iraq war depths. His father had a similar thing happen, thanks to the 1991 Persian Gulf War. But Obama has moved in a tight orbit just under 50 percent, so much so that that we had to enlarge the height of his graph to accommodate the regularity with which those poll numbers occurred.

Why did this happen? Because his approval ratings among Democrats and Republicans barely budged either.

Barack Obama has been a very polarizing president. Republicans always hate him. Democrats always love him. And independents -- many of whom, remember, are independent in name only -- always sort of feel indifferent.

Giving Barack Obama one of the least volatile approval ratings in modern history.