How Enthusiasm, Early Voting Can Affect Turnout in Presidential Election

— -- The fluctuating enthusiasm surrounding the two leading presidential candidates could have a big impact on voter turnout in this election.

Increasing use of early voting and largely increasing overall turnout in the past several general elections may contribute to a record number of people voting, according to ABC News political analyst Matthew Dowd.

"As a percent of voting age population it will be low, probably lower than the past four or five presidential elections," Dowd said. "Net total will set a record though."

When it comes to the specific impacts on the campaigns, Dowd says that Hillary Clinton's staff "needs to focus all campaign efforts on turnout," but he doesn't think that turnout levels will effect Trump's bid.

"It could affect down-ballots though, if GOP voters aren't enthused," he said.

The latest ABC News tracking poll released this morning shows that while 56 percent of Clinton's supporters said that they are voting for her because they want to see her in the White House, 54 percent of Trump supporters said that they are voting for him more as a referendum on Clinton than as a reflection of their view on Trump directly.

"When you look at the enthusiasm numbers for each candidate they are below 2012, 2008, and 2004," Dowd said.

An estimated 34 percent of voters are expected to vote early, according to Michael McDonald, a political science professor at the University of Florida and fellow at Brookings Institution. McDonald told ABC News the steep climb in early voting over recent decades is due to states making early voting more widely available, along with incremental year-to-year increases as voters become more familiar with early-vote procedures.

Thursday Oct. 20 was the first day of early voting in North Carolina this year, and while the number of votes on that first day was several thousand lower than the 2012 presidential election, there were still 164,207 votes received, according to the state's board of elections.

In Georgia, voting began on Oct. 17 and there have been at least 432,696 votes cast both in person and by mail-in ballot, according to the secretary of state.

The number of Americans casting ballots overall rose slightly in recent presidential elections. A four-decade high was reached in 2008 when Barack Obama was first elected president, with 58 percent of the electorate voting, before declining slightly in 2012 to 55 percent, according to the Federal Election Commission.

In 1996, when Bill Clinton was elected to a second term, it was the first time since 1924 that less than 50 percent of the electorate — 49 percent — went to the polls.

ABC News' John Kruzel contributed to this report.