Thirty million votes are already cast for the next president of the Unites States, and the turnout so far favors President Barack Obama over GOP challenger Mitt Romney.

The contest for the White House has hardly begun, however: These results, from 34 states and the District of Columbia, account only for the party affiliation of those who have voted early. This obscures all those coveted independent voters that may defy loyalty with their registered party, a major factor in deciding such a tight election.

According to data collected by the Associated Press, key states such as Iowa, Florida, Ohio, Nevada and North Carolina see greater Democratic turnout, with the president's campaign adviser David Axelrod expecting Obama to preserve many of these leads into Election Day.

In North Carolina, the president leads Romney in early votes by 16 percent, in Iowa, 11 percent. It's much closer in other key states such as Ohio, where Obama leads by 6 percent, or Florida, where he's ahead by a mere 3 percent.

Yet there have also been reversals for the president: In Colorado, where the president won by nearly 9 percent in 2008, Republicans have the edge.

Other factors besides the independent vote color these results: Republicans often turn out with much greater enthusiasm on Election Day. Also, in this election there's been a closing of the gap in turnout in battleground states, and the combination seems to favor Republicans.

Ohio is a clear example. Monday on CNBC, Romney supporter and the state's Republican senator, Rob Portman, boasted that the net gain of early votes for his party this year, in his state, is about 200,000.

Still, without a clear portrait of the independent vote, there's no way to tell what surprises are in store for each battleground state. A clear view won't arrive until the final moments of election night.