What they’re really measuring, of course, is which one’s the worst president. It’s still G-Dub — by a hair.

By 47 to 45 percent, Americans say Obama is a better president than George W. Bush. But that two point margin is down from a 23 point advantage one year ago.

“Democrats may want to think twice about bringing up former President George W. Bush’s name while campaigning this year,” says CNN Polling Director Keating Holland.

“But that doesn’t mean that Americans regret their decision to put Obama in the White House in 2008. By a 50 to 42 percent margin, the public says that Obama has done a better job than Sen. John McCain would have done if he had won. And by a 10-point margin, Americans also say that Joe Biden has done a better job than Sarah Palin would have done as vice president,” adds Holland.

Is the lesson from this poll really that Dems should think twice before bringing up Bush? The most amazing thing about it is that, after more than a year and a half of economic misery and trillion-dollar health-care boondoggles and giant oil spills and slow going in Afghanistan, The One is still (barely) preferable to Dubya. The sour aftertaste of the Bush era lingers on even after devouring a big Hopenchange shinola sandwich, and no one — including tea partiers who grumble about Bush’s big-spending ways — is doing much to try to change that. The determining factors here, I think, are that Obama’s still not even halfway through his first term and did, after all, come into office after the financial crisis was already in full swing. To wit, this Marist poll out today finds that only 33 percent say current economic conditions are due to his policies compared to 61 percent who say he inherited them. The public’s fully prepared to render a verdict on Democratic control of government next month but they’re not quite ready yet to render a verdict on The One himself, which is why we also get this fantastically depressing tidbit from Marist:

Despite the president’s 43% approval rating, a majority of voters — 51% — think the president’s approach will eventually solve the problems facing the nation. But, he needs more time. 45% report Mr. Obama’s approach will not solve the nation’s problems. Four percent are unsure.

Not surprisingly, there is a partisan divide on this question as well. 81% of Democrats think the president’s approach needs more time while 15% say his efforts will be futile. On the other hand, 76% of Republicans think the president’s approach will not fix America’s problems compared with 20% who say patience is in order. A majority of independent voters — 54% — report the president’s approach will not fix the problems facing the nation while 42% think they will in time.

Even 20 percent of the GOP — let’s call them, oh, I don’t know, “Charlie Crist Republicans” — aren’t ready to write Obama off just yet. But give ’em time: I suspect that 51 percent figure is down from something like 70 percent at around the time of the inauguration, which if true would mean he’s shedding around a point per month. If unemployment doesn’t inch down next year, you can imagine where his numbers will be come election time 2012.

Elsewhere in the CNN poll, the GOP leads 52/45 on the generic ballot and by two to one among independents. Prepare for utter destruction three and a half weeks from now. Exit question: Why does Bush rate higher than McCain or Palin in the poll given that he ended his term less popular than either of them? Is he benefiting a bit from the presidential aura, or is it simply that people are more likely to think of him when they remember better economic times a few years ago? Or is it the fact that he’s handled himself so well over the past 20 months? Quote: “I loved being your president. But frankly, I’m having the time of my life not being your president. I do not miss the limelight. I have zero desire to be in the press. I have zero desire to be on your TV screens. Eight years is enough of that.”