Before the polls open on Election Day, more than 29 million Americans will have already cast their ballots in early voting.

But a number of states have yet to report their totals. Michael McDonald, a professor and elections expert at George Mason University in Virginia, expects some 40 million ballots to be cast or mailed before Election Day.

In the presidential race, supporters of Sen. Barack Obama, including many black voters, have been voting in high numbers, McDonald said Monday in a WashingtonPost.com chat.

“What we are seeing is that Obama supporters do tend to be voting early more than McCain supporters, which is showing up in the polls and the partisan registration numbers. The other interesting group that is participating at really unprecedented levels are African-Americans. If these numbers hold through Election Day, their turnout percentage could exceed that of white voters. The share of African-American early voters is running about 8 percentage points greater than in the 2004 electorate.”

Many voters across the country have endured hours-long waits and voted in record numbers.

In Florida, more than 2.6 million voters cast early ballots, the Miami Herald reported. One person voted at 12:45 a.m. Monday — after standing in line for nearly nine hours at Miramar City Hall.

Election officials in Georgia have processed triple the number of early ballots compared to just four years ago, McDonald said. Even though that resulted in long waits there, many voters remain upbeat about participating in this historic election and avoiding lines that could be even longer on Election Day, as evidenced in this video from Cobb County, Ga., submitted to the Online NewsHour/YouTube Video Your Vote project.

McDonald said it will be interesting to watch the Election Day wait times in states that do not have no-excuse absentee voting, such as the political battlegrounds of Missouri, Virginia and Pennsylvania.

“It could be that after this election, we’ll look back on Election Day at long lines in states with little early voting, and those states may re-evaluate and adopt early voting,” McDonald said in the Post chat.

Before that happens, the Christian Science Monitor’s editorial board advised caution on expanding early voting, saying its advantages might be outweighed by actual or perceived problems such as lost ballots, fraud, changing circumstances and dissuading people from voting later based on early estimating tallies.