When Republican U.S. Senate candidate Mike McFadden strode into St. Paul's State Office Building to file his candidate paperwork, he greeted the waiting media and more warmly greeted the two Democratic trackers that follow his every move.

McFadden said he sees them everywhere.

"I do see them. Both Emilio (Barrientos of American Bridge) and Teddy (Tschann of the DFL.) I've seen them all the state. They work hard," McFadden said.

Trackers are the young partisan staffers who record candidates wherever they go to aid in opposition research, hoping to catch their prey in an off message moment.

Barrientos and Tschann said McFadden has been pretty good to them.

McFadden says the same of his Democratic, camera-wielding shadows.

"That's part of the process. It's what I've signed up for. They've been very respectful," McFadden said.

That respect sometimes grows.

Democratic U.S. Sen. Amy Klobuchar's 2006 Republican tracker Ryan Flynn became a 2012 supporter when she ran for re-election.

But the relationships are not always so smooth.

In 2010, Mark Dayton, then running for governor, complained that his GOP trackers followed him so closely that they made it impossible for him to greet Minnesotans at Game Fair.

The GOP used the complaint to pound Dayton for having a, "bizarre, weird, erratic reaction" and hit back by having their trackers don T-shirts proclaiming, "I'm with the guy who wants to raise your taxes."