The White House has to like the top-line results from the latest NBC/Wall Street Journal poll, which shows Barack Obama getting an eight-point bounce over last month to 53% and 41% disapproving.   It’s the first time in eight months that Obama has had a positive approval gap, since May’s 48/45.  However, as the WSJ reports, the survey took place in the immediate aftermath of the Tucson shooting and memorial, which may make this rise transitory:

Surges in presidential popularity are common after a galvanizing national tragedy, said Bill McInturff, a Republican pollster who co-directs the Journal/NBC News poll with Democrat Peter Hart. Bill Clinton saw a four-point jump after the 1995 Oklahoma City bombing. George W. Bush saw a surge after the Sept. 11, 2001, attacks.

But those bounces can be fleeting. Mr. Clinton’s faded in a month amid partisan arguments over the budget. Mr. Bush’s lasted as the nation shifted onto a war footing.

The poll’s methodology is rather interesting as well.  NBC/WSJ’s pollster, Hart/McInturff, polled 1000 adults without restricting respondents to registered or likely voters.  In fact, 19% of those responding claimed not to have voted in the 2008 elections, which is almost 1 in 5 and tends to make the predictive value of the poll rather weak. The D/R/I sample split is 31/21/39, a ten-point Democratic advantage when Gallup and Rasmussen both show the electorate evenly split or with Republicans taking a slight edge in affiliation.  A 21% sample composition for Republicans is a gross underrepresentation.  The previous poll has a 33/23/36 split.

On top of that, 42% of respondents say they voted for Obama, and 29% for John McCain, while 10% split evenly say they voted for someone else or can’t recall for which candidate they voted.  Since Obama beat McCain by seven points in the popular vote, this appears to oversample Obama voters badly.  Compare this sample to their previous poll, in which the split was 41/32 and 17% said they didn’t vote for anyone at all, and one can see where at least some of the bounce originates.

Otherwise, like the WaPo/ABC poll earlier this week, the bounce appears confined to personal considerations and not the issues.  On the economy, Obama went from 42/54 to 45/50, which almost exactly fits the change in sample between the two polls.  Oddly, the poll only asked about one other issue — Afghanistan.  Obama’s numbers were virtually unchanged on the war.

Nothing in this poll points to long-term strengthening in Obama’s polling.  Now that Congress has returned to work, Obama’s low polling on the issues will once again drive his overall job approval.