In 2008, Obama won 53 percent of the vote, the highest percentage for any Democratic nominee in history except Andrew Jackson, Franklin Roosevelt and Lyndon Johnson. Now he's averaging 46 percent in recent polls.
That's much closer to the 45 percent that Democratic candidates won in elections to the House in 2010. And in the last three presidential elections, the winning candidate has won the same percentage (or within 1 percent) as his party's percentage in House elections two years before.
Obama had a popular vote margin of 7 percent in 2008. But Republicans had a margin of 7 percent in the popular vote for the House in 2010. If you tote up the electoral votes in the states they carried, you would find them with a 351-184 edge over Democrats (the remaining three in the District of Columbia are obviously Democratic).
When you look at target states, you see the same picture. Take Gallup's 12 swing states, which in its most recent survey together favored Obama over Romney by 47 to 45 percent. That's a lot less than the 53 to 45 percent by which he carried them four years ago.
In recent state-by-state polling, Obama leads in all 12 but averages more than 50 percent only in New Mexico and Wisconsin. And in all 12 he's polling less than the percentage he won in 2008.
There are big drop-offs in Pennsylvania and New Hampshire, where Obama owed his victory to big margins among affluent suburbanites -- Mitt Romney's strongest demographic in the primaries.
His smallest drop-off is in North Carolina, which he carried only 50 to 49 percent but where voters seem sharply polarized. It's a particular target for Obama, who chose Charlotte as the site of the Democratic National Convention.
Romney is running even in recent Florida polls and less than 5 points behind in Iowa, New Hampshire, North Carolina, Ohio and Virginia -- within striking distance. If he wins them all plus safe Republican states, he'll be elected.
That's without Colorado, Michigan, Nevada, New Mexico, Pennsylvania and Wisconsin, with 66 electoral votes in all, which could conceivably be within Romney's reach.
Democrats hope to expand the field to Arizona, with 11 electoral votes, and Republicans hope to expand it to New Jersey, with 14. Those hopes may look dim now, but at this point in 2008 few expected Obama to carry North Carolina or Indiana.
The bottom line is that at this point Obama doesn't have an Electoral College lock. Neither does Romney. The numbers tell us that this election is up for grabs.
The Obama campaign has prepared for a long, hard slog through the target states. The Romney campaign is getting prepared for the same.