Sens. Russ Feingold of Wisconsin and Michael Bennet of Colorado are just two incumbents locked in tight re-election races in states where local officials have warned they will likely not be able to ship out general election ballots to overseas military voters by the Sept. 18 deadline.
Both Democrats' race are listed as "toss-ups" by RealClearPolitics.com, and military ballots could make the difference.
But Wisconsin and Colorado are among 10 states where local officials say they may not be able to comply with Move Act provisions that call for ballots to be mailed out at least 45 days before the 2010 midterm election.
Fox News has identified four states -- Wisconsin, Colorado, Maryland and Washington -- where races may hinge on those absentee ballots and on whether their delivery works as intended on behalf of the fighting men and women abroad.
"Russ Feingold's election in 1998 was decided by fewer than 40,000 votes. This time around, our polls are showing him leading by one (percentage) point or maybe down by one point," said Sean Trende of RealClearPolitics.com. "So there is a chance that the 15,000 or so overseas military ballots could be what decides that election, if it ends up within 1,000 votes, which is entirely possible."
And in one Maryland congressional district, Frank Kratovil, a Democratic freshman, also faces a tight race for re-election.
Kratovil "was behind on Election Night 2008; and after the absentee ballots, including the military and civilian overseas absentee ballots (were counted), he won the election by 3,000 votes," said Chip Levengood, chairman of the Overseas Vote Foundation.
But on that night in 2008, roughly 63 percent of America's registered voters actually turned out to the polls -- compared to only 54 percent of military voters.
But when the military's disproportionately high population of young males is factored in, the Pentagon scores the uniformed voting participation rate at 73 percent, 10 points higher than the nation as a whole and on par with the most reliable demographic -- the elderly.
"Active-duty military always has an insight into world situations that maybe others do not. Their perspective is significant. Whether it is for one party or another isn't really the issue; it's that their vote is significant," said Jessie Jane Duff of Military Voting Rights USA.
Some of the ten waiver states -- include Alaska, Colorado, Delaware, Hawaii, Maryland, Massachusetts, New York, Rhode Island, Washington, and Wisconsin (as well as the District of Columbia and the Virgin Islands) -- will accept overseas military ballots after Election Day to make up for the fact they can't send them out by Sept. 18. But in the case of competitive states like Wisconsin and Colorado, it's still less time than the 45-day transmission period mandated by the Move Act.
Late Thursday, Maryland elections officials said they no longer need the waiver. State elections board administrator Linda Lamone said the Defense Department found Maryland in compliance with the law's 45-day mandate.
Lamone said Maryland will expedite delivery of full ballots to military and overseas voters and give absentee ballot requests priority.
Fox News' James Rosen contributed to this report.