How could this have happened?  For one thing, the CBS/NYT poll no longer gives the Democrats a double-digit boost in its sample, although they’re still putting their thumbs on the scale.  But even more than that, the electorate simply is becoming less enchanted with Obama the longer he’s in office, and on what used to be key Democratic issues:

President Obama’s job approval rating sits at 50 percent in the latest CBS News/New York Times poll, the lowest level it has reached in CBS News polling.

The president still has a net favorable rating, with 50 percent approving of his performance and 39 percent disapproving. But as Mr. Obama has confronted challenges ranging from the economy to the war in Afghanistan to health care, public perception of his handling of his job has steadily fallen.

In April, Mr. Obama’s approval rating was 68 percent. By August, it was down to 56 percent. It dropped to 53 percent last month before falling another three points in the latest poll.

Democrats still largely back the president, with 82 percent expressing their approval. Just 19 percent of Republicans approve of his performance, however, and independents are split: 43 percent approve of his performance and 41 percent disapprove.

Americans cite the economy as the issue most important to them, and on that issue the president’s approval rating has been in decline. It now sits at 47 percent, down two points from last month and down seven points from October.

In this sample, Democrats only have a nine-point edge over Republicans, as opposed to the normal 14-15 point edge.  That’s still far too high, of course.  Gallup has the party identification gap down to six points, and Rasmussen’s latest survey has it down to half of that.  But that’s not the only reason to suspect the CBS/NYT polling methodology.  That gap is from the adjusted sample.  Here’s the data from before and after the adjustment:

Before the “adjustment,” Democrats had a seven-point lead over Republicans and a slight disadvantage to independents, which comes close to the split shown in the Gallup poll from last October.  After the adjustment, Democrats wind up with a nine-point advantage over Republicans, which is two points higher than Obama got in winning the election 13 months ago — when he won plenty of independents and crossover Republicans.

Even with that kind of bias, Obama’s numbers are declining rather obviously.  As the CBS report notes, Obama had a 68% approval rating eight months ago, but health care and the economy have dragged him down.  Before Obama’s election, those two issues were perennial powerhouses for Democrats.  Now Obama is underwater on health care, 42/50 even with the boost of Democrats in the poll, and within the margin of error on the economy, 47/43.  On Afghanistan, a majority of 51% approve of sending more troops, but 55% disapprove of Obama’s publication of timetables on the surge, so he’s not winning on the traditional Republican issues, either.

And how do people think we should fund that war effort?  Only 10% say “tax increases.”  Fifty-three percent say “spending cuts.”  If that’s what a majority of Americans want, they’re not going to get it from this Congress and this President, and Obama can expect the next CBS/NYT poll to get even more unfriendly.