Jim McTague of Barron’s devotes his latest “D.C. Current” column to the recent congressional rush to flee the nation’s capital.

Ballots away! Voting in the 2014 midterm elections has already begun by mail in many states with the casting of absentee ballots. Prognosticators pay close attention to this early action — and with good reason. By the end of October, candidates ahead in early balloting are likely to win if polls also show them leading, says George Mason University’s Michael McDonald, who has been doggedly following early voting since the 2008 election.

Between 30% and 50% of the midterm’s votes could be cast in early voting, according to Rick Hohlt, a Republican consultant. That’s why members of Congress have been in a rush to get out of Washington. “To get free media, you have to be home,” says Hohlt. Campaigning politicians are desperate for local-media coverage that enhances their image during early voting.

North Carolina already has begun posting data. As of last week, 958 votes had been cast out of 11,201 requested absentee ballots, mostly for Democrats. The early voting confirms polls that put U.S. Sen. Kay Hagen, a Democrat seeking a second term, slightly ahead of GOP challenger Thom Tillis. McDonald posts early-voting data at electproject.org.

Of course, it’s safest to wait until Oct. 31 before jumping to conclusions. In 2010, when Nevada Sen. Harry Reid was running for re-election against Tea Party candidate Sharron Angle, he was down in early balloting until the very last week before the election. Then, suddenly, he surged ahead.

Early voting by mail generally favors Republicans everywhere but Iowa, where Democrats have a superb get-that-ballot-in-the-mail machine; and early voting at polling places tends to favor Democrats, McDonald says. The 2008 general election was an exception to the rule, with early balloting by mail favoring Barack Obama. The pattern reverted to trend in 2010 and 2012.