He trails by 7 points among whites, a group no Democrat has won in exit polls dating back 32 years. Closest were the party's winners, Jimmy Carter in 1976 (-5 points among whites), Clinton in 1992 (-1) and Clinton in 1996 (-3).
Obama, in particular, is doing better than the recent Democratic norm among middle- and upper-income whites. And after trailing last week he's moved into a dead heat among white Catholics, like independents another usually swing-voting group.
Kerry lost them by 13 points, Gore by 7. Carter and Clinton won white Catholics by 5 to 7 points.
Obama's standings now do not predict the vote next week, and given the differential among groups turnout is critical.
It's also a moving target given the number of early and absentee voters: Thirty-four percent of likely voters say they'll vote early or by absentee ballot; as reported last week, it's a group that heavily favors Obama, now by 59-39 percent. So do first-time voters, who are mainly under 30.
Contrary to some expectations, ABC/Post tracking data does not show disproportionately higher turnout this year among first-time and young voters, or for that matter among African-Americans. Their projected turnout levels instead are within a point or two of what they were in 2004.
The biggest change is in partisanship.
As covered in previous tracking reports, voters in 2004 divided evenly in party allegiance, 37-37 percent, with the rest independents.
In this poll 37 percent are Democrats, 32 percent Republicans -- reflecting generally declining Republican allegiance over the past five years.
McCain's challenge, then, is to overcome not just the heavy weight of the economy, but also the five-year trend in partisanship that's followed the unpopularity of the Iraq war and the concomitant rise in George W. Bush's disapproval rating, to the highest on record for a president in 70 years of polling.
METHODOLOGY: Interviews for this ABC News/Washington Post tracking poll were conducted by telephone Oct. 23-26, 2008, among a random national sample of 1,314 likely voters, including landline and cell-phone-only respondents. Results have a 2.5-point error margin for the full sample. Sampling, data collection and tabulation by TNS of Horsham, PA.