Chicago, Ill. (CNN) Rep. Tammy Duckworth made her expected challenge to Illinois Sen. Mark Kirk official with a video announcement on Monday.

"I'm running for the United States Senate in 2016 because it's time for Washington to be held accountable and put Illinois' families and communities first," Duckworth says in the YouTube video . "If you elect me as Illinois' senator I will fight my heart out to represent you with honor and integrity."

The video highlights her humble upbringing and frames the second-term Democrat as a daughter of a Marine, a wife and a mother.

The two contenders have some unique similarities — both are military veterans, Duckworth of the Army and Kirk of the Navy, and both at times use wheelchairs to get around Capitol Hill. Duckworth suffered the loss of both her legs when a helicopter she was piloting was hit by a grenade, and Kirk uses a cane or a wheelchair to get around following a stroke that took him out of commission in the Senate for months.

But their race is certain to be one of contrasts, as Kirk is seen as the GOP's most vulnerable incumbent this cycle because of the deep-blue tint of Illinois, especially in presidential cycles. While Duckworth is considered a top-tier challenger, she could face a battle for her party's nomination, as a handful of other Illinois members, including Reps. Robin Kelly and Bill Foster, are contemplating bids.

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