Based on this estimate, Obama has the second greatest rate of decline, losing 1.6 percentage points of approval each month. Clinton did worse, falling at a monthly rate of 2.3 points. If you look back to the first figure, you see that Clinton fell faster and further, but then rebounded a bit at the end of the summer, making his net change a little smaller (-14) but his overall rate of decline a bit steeper. Obama's chart shows two phases, an initial shallow decline with a bit of a rebound and a more recent decline at a higher rate. Linear fits don't distinguish between these details. But it is pretty clear that based on the linear trend, Clinton fell faster than Obama, contra-Brooks.
What is more interesting is how many presidents managed only slight declines or even gains in the first 8 months. Carter and the second Bush both lost just over a half point per month. Kennedy, Nixon and Reagan all gained, from 0.1 to 0.2 points per month. Eisenhower gained an impressive 0.65 points per month, and the first Bush gained an astonishing 1.9 points per month. So no, not everyone falls off. But yes, Obama has fallen, and quite badly in comparison. Just not quite the absolute worst.
We might put Obama's trend in perspective of his predecessors as well. The next chart shows the trends for all these presidents, highlighting Obama.
This chart offers one important corrective to a widely repeated myth: Obama was not "wildly popular" at the start of his term. This exaggeration is repeated so often that it is becoming a universal "truth". But the fact is Obama entered office with strong support, but not so strong as that of Eisenhower or Kennedy, and after a couple of weeks his approval was above average but only by a bit. It is this myth that adds to the drama of his current fall, but the myth exaggerates how high in the pantheon Obama first stood.
The second useful perspective of this chart is that much of the decline has come after 3.5 months, or starting in May. The decline since then has been quite steady, dropping Obama from a shade above average at 3.5 months, to a next-to-last place now. This second slide should be far more worrisome to the White House than the initial polls or the net change from first to last poll.
Finally, we should remember that the first 8 months do not tell the future. Clinton ranks dead last as of September 1, yet finishes with one of the highest approval ratings, and maintained high approval for longer than anyone since Eisenhower. Nor could GW Bush's approval on 9/1 say anything about his approval following 9/11.
The best perspective is the full term, and with time marked by elections rather than months. The chart below provides this for all presidents since FDR's 3rd term. The scales are exactly comparable across presidents so your eye can show you differences in trends. And the vertical blue lines mark off mid-term and presidential election dates. Those are the moments that matter. A low approval on November 2, 2010 will push Democratic losses in the House well above 20 seats. But a rebounding approval (driven by a better economy) can hold those losses below the historic average. That is the future still in Obama's hands to write. And that is basically what David Brooks was saying to the White House.