The "70-30 issue" is a cliche in political circles: Basically, the idea is that there are all sorts of issues where 70 percent of Americans are for X and 30 percent are against X . . . . The trick for most/many politicians is to always be on the 70 side. . . . When you look at Obama’s troubles, it’s kind of shocking how he’s managed to maneuver the party to the 30 percent position (or allowed it to drift that way) on so many issues.. . . One question I have, and maybe brother Geraghty or someone else around here knows the answer, is whether Bush got himself in a similar mess.
I don't think 70-30 applies, really. The matter is more one of the reception of leadership.
George W. Bush's approval — and mandate — collapsed when both the left and right anathematized the president over Katrina, and the general public was shocked by the disaster enough to have listened. Before that, the contention of Iraq slowly abraded Bush's ratings as a majority of Americans held fast to the hope that they were right in originally supporting the operation.
If a parallel can be drawn, it's between Iraq and the economy (an unfair comparison considering the gravity of the war, but as we know from the Nineties, different times trade in different values). Most Americans continue to hope that their leader a) intends to improve their quality of life, but more importantly b) is actually capable of doing so. Economic illiteracy plays some role, here: media and education have left many confused about how markets actually work, so unless splashed with cold water by a truly ideological GOP, the electorate is unlikely to summarily reject both tax-and-spend and its advocate president.
The point commencing a terminal fall in public approval will almost certainly lie, very unfortunately, in President Obama's inability to respond to the kind of exigency that only happens once every ten years or so. Second/Third World invasion (Carter, failed; H.W. Bush, passed)? Massive terrorist attack (Clinton, W. Bush; both passed)? Dishonor (Nixon, failed; Ford, arguably failed)? Unsupportable war (Truman, Johnson; both failed)?
Absent such an event, missteps here and there are small stuff. Obama may preside over a solidly Republican congress, but preside he will.