Look at the demographics of the poll.
ABC News/Washington Post Poll--Always read the demographics: Vote preferences among groups, as noted, include Romney’s best showing to date among registered voters who identify themselves as independents, 53-39 percent. Obama comes back to parity overall because Democrats account for a larger share of the pie than Republicans, 36 percent of registered voters vs. 27 percent. Overall the poll was a tie. So if Democrats don’t show up at the polls with 9 percent more people than Republicans, Obama loses big.