Here’s something to feed your jitters: three new polls on Pennsylvania, all showing Obama ahead by just 4-5%.

How should we regard them? And will the electoral fate of Pennsylvania matter in the big picture anyway? First, a rundown of the polls in question:

• Thursday saw the release of an NBC/Mason-Dixon poll that had Obama ahead by just 4 points, 47% to 43%.

Not reassuring: The last time Mason-Dixon polled the state was in mid-September, when it had Obama ahead by 2. At the time (McCain was still riding his post-Convention bounce), that was comparable with what other pollsters were finding: six other polls conducted around the same time ranged from a tie to a 5-point Obama lead.

Possible comfort: The poll was of a mere 625 likely voters, making for a relatively high 4% margin of error.
Possible comfort: Mason-Dixon, Nate Silver pointed out, “has .. had a Republican “lean” this cycle of perhaps 2-3 points. They are quite frequently the most favorable number for John McCain in any given state.”

The Pollster.com trendlines for the state since 4 February, when Internet polls are filtered out and the trend smoothing is set to more sensitive.