There aren't really any unifying issues in this year's midterm elections, except for one: the treatment of the nation's veterans.

In 2010, it was Obamacare that dominated the airwaves. This year veterans, and the Veterans Affairs scandal, have risen to prominence in both parties' ads.

"It has been the one big breaking news story of 2014 that's actually reverberating in campaign ads in a widespread way," says Elizabeth Wilner, vice president of Kantar Media Ad Intelligence, which tracks political advertising.

"We don't see foreign policy events, the crisis in the Middle East, even border security here at home appearing in campaign ads to nearly the same degree," she says. Wilner says as of last month, some 34,000 veteran-themed ads had run in races nationwide.

Candidates are using the VA problems in their ads in different ways. For Republican Rick Allen, who is running for a congressional seat in Georgia, it's another in a string of Obama administration woes:

But most campaigns seem to be using the VA scandal as a standalone problem. Jackie McPherson is a Democrat running for Congress in Arkansas, and his ad features a Vietnam-era veteran dealing with post-traumatic stress disorder:

It may seem like candidates for Congress are spending a lot of money to win over veterans, a relatively small segment of the electorate. But what they're really after are votes of undecided and independent voters, says Jon Soltz, chairman of VoteVets.org. He says it's because veterans affairs are a "mom and apple pie issue."

Vote Vets is a Democratic group that's spending $5 million to unseat Senate Republican leader Mitch McConnell in Kentucky. Soltz blames McConnell for blocking a $21 billion measure aimed at increasing VA funding. The group is running this ad featuring a Vietnam veteran, shown slowly walking with a cane:

Republicans have their own groups, among them Concerned Veterans for America, which is backed by the Koch brothers. Here's an ad they're airing in Iowa, attacking Democratic Rep. Bruce Braley, who's running for the Senate:

Dan Caldwell, issues and legislative campaign manager for Concerned Veterans, says this spot and one the group is running in North Carolina targeting Democratic Sen. Kay Hagen are aimed at holding Democrats accountable.

"Congressman Braley and Sen. Kay Hagen have something in common. They both campaigned on being veterans advocates, they were going to help fix the VA. But once they got into office, the situation at the VA got worse and they didn't really devote enough attention to it," he says.

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