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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.

Her announcement, however, already started to winnow the field. Rep. Cheri Bustos, who had been considering a bid, didn’t endorse Duckworth outright but said in a statement that the congresswoman “clearly has the priorities we need in our next U.S. Senator.”

“I can’t see jumping into a race at this time when we already have such a strong fighter for working men and women and veterans,” she said.

“We’ve got a deep bench of strong potential candidates in Illinois, many of whom are friends and colleagues. I’m not making any formal endorsement at this time. But if you look at Tammy’s record of standing up for American manufacturing, for working women and their families, and for our veterans, it’s clear to me she fights for the things that are important to my constituents.”

The National Republican Senatorial Committee framed Duckworth as an ideologue and tied her to imprisoned former Illinois Gov. Rod Blagojevich.

“Congresswoman Duckworth is a partisan politician who got her start in politics as a result of Rod Blagojevich’s political maneuvers,” NRSC spokeswoman Andrea Bozek said in a statement.

“Unlike Congresswoman Duckworth, who has put her extreme policies in Washington before Illinois families by voting with Nancy Pelosi 92% of the time, Mark Kirk has been an independent voice. Senator Kirk’s record of accomplishment and thoughtful independence will outshine any candidate that emerges from the Democrat primary in Illinois.”