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Washington CNN —  

Arizona Sen. John McCain will get a top-tier challenger in his bid for re-election later this year now that Democratic Rep. Ann Kirkpatrick has decided to run for the Senate.

“I love this state, and I’ve worked hard all my life to put Arizona first,” Kirkpatrick said in a statement announcing her bid on Tuesday. “From the timber towns of the White Mountains to the tech hubs of Phoenix and Tucson, we are working to build a strong, diverse economy. I’m fighting for Arizona every single day, and I’d be humbled to represent our state in the United States Senate.”

The third-term Democrat beat the odds last cycle by winning re-election in a red-leaning seat despite a tough political climate that swept similar Democrats out of office nationwide. She did so without backing down from her support of Obamacare, which proved toxic for other, more seasoned Democrats, and by emphasizing her local roots and Native American ties.

Her moderate profile will give her a boost in what’s sure to be a challenging race from the start. Democrats believe McCain to be vulnerable because of his five-term tenure in the Senate, and he’s expected to face a primary challenge that could leave him weakened for the general.

But Arizonans haven’t elected a Democratic senator since the late 80s, and the state has voted Republican in the last four presidential elections.

The National Republican Senatorial Committee attacked Kirkpatrick in a statement, tying her to President Barack Obama and saying she “made life worse” for Arizona families.

“Ann Kirkpatrick has been part of the problem in Washington and Arizonans are paying the price. She doesn’t believe we should ‘second guess’ President Obama which is why she supported Obamacare, his trillion dollar stimulus that created jobs in China and cuts to Medicare,” said Andrea Bozek, communications director for the committee.

A potential Democratic gain in the Senate is also the party’s loss at the House level – Kirkpatrick’s decision to run opens up a GOP-leaning seat that they’ll be hard-pressed to defend.