A public approval rating of 28% is of concern only if your constituency is the American public. But we know that for Bush the public is merely a group that needs to be periodically bamboozled, is no longer of any use to him, and is basically irrelevant from here on out. Bush's real constituency is the collection of special interest groups that fund the Republican Party, and viewed this way he can see his administration as a success. This explains Bush's seeming lack of concern for approval ratings.
The special interest groups backing the Bush administration are doing well, and receiving a good return on their investment in him. Namely,
The HMO's are doing well with their government-subsidized Medicare Advantage plans.
The pharmaceutical industry is bolstered by a Medicare Part D that minimizes competition and keeps drug prices high.
The defense industry is bolstered by record spending on defense.
Wall Street did not get Social Security privatization, but got low tax rates on dividends and capital gains that have kept the stock market elevated.
Beltway parasites like Halliburton are feeding at the Iraq hog trough to the extent of 10's of billions.
The energy industry has record energy prices and stonewalling on global warming.
Depending on your perspective, the Bush administration can be regarded as a huge success. The American public is not and has not ever been a constituency of this administration, and whether or not it approves of Bush is perfectly irrelevant at this stage.