(AP Photo/Robert F. Bukaty)

In 2008, about 30 percent of the national vote was cast via early or absentee ballots. This year, the expectation is that about 40 percent of Americans will cast a vote early, observers said.

"The big picture is [that] early voting is up," said Michael McDonald, director of the United States Elections Project. "More Republicans appear to be voting early [than in 2008], and Democrats are also voting early."

More than 7.7 million people nationwide have cast a ballot already, McDonald calculated.

There appear to be two reasons for the increase, he said.

First, the Romney campaign is doing a much better job of mobilizing the early vote than the McCain campaign did. The McCain campaign did very little to mobilize the early vote in 2008 and it was vastly outnumbered by the Obama campaign.

This cycle, the Republican National Committee reports that Republicans are making up a larger share of the early voters than they did last cycle - and they've put a comprehensive program in place with 119,000 volunteers who have made 44.8 million contacts total since the spring.

The other reason for the increase may be that voters find early voting convenient.

Here is a closer snapshot of where things stand in the battleground states where in-person early voting is allowed.

COLORADO

A total of 325,810 votes have been cast so far - 126,539 from registered Republicans and 120,965 from registered Democrats, plus 75,030 from "unaffiliated" voters.

FLORIDA

So far, 925,604 mail-in absentee ballots have been cast - 414,016 from Republicans and 363,881 from Democrats. Early in-person voting has not started yet in Florida. It kicks off on Saturday, Oct. 27.

IOWA

Voters have cast 399,858 ballots in the state - with 183,780 from Democrats and 126,872 from Republicans. Democrats currently have the advantage, but Republicans said they were performing much better than they were in Iowa at this point in 2008. At the same point in 2008, Democrats had about a 24-percentage-point lead in the early vote, Republicans said, whereas this year it's about 8 percentage points.

NEVADA

Democrats boast the advantage over Republicans - 101,935 to 79,058 - among the 218,616 votes cast so far statewide.

OHIO

A total of 808,051 ballots have been cast so far - with 618,861 absentee ballots returned and 189,190 additional in-person votes. Ohio does not register voters by party. Numbers are up in rural and urban counties, which bodes well for both Republicans and Democrats.

VIRGINIA

Virginia allows for in-person ballot casting ahead of Election Day - but state officials call it it in-person absentee voting and voters need an excuse to do it.

In any event, 247,862 votes already have been cast. The state does not register by party, but the Obama campaign reported earlier this week that more ballots have been cast in precincts Obama won than precincts McCain won. However, the Republican National Committee pointed out that absentee and early voter activity is down from 2008 in the Democratic counties of Alexandria, Arlington and Fairfax, and it's up in Republican-leaning Loudoun County.

WISCONSIN

Wisconsin is the great unknown. Every municipality in the state handles its election procedures differently. There are more local election officials in Wisconsin than in the entire rest of the country combined. As a result, the state doesn't report out complete numbers of their early and absentee votes as they come in. To make matters even more vague, voters don't register by party in Wisconsin either.