Interesting enough, I just read today that americans calling themselves liberal are only 20% of the population, while those calling themselves Conservative are 34% and Moderate is at 45% (I guess the other 1 percent are just clueless). Given the poll number from CBS that you show and the results, if we weight them to be indicative of the population at large, we see that instead of 38%, Bush is actually at 48%.
So much for "BlatherGate" CBS and objective reporting.