Updated, 2:05 p.m. | Arizona Rep. Ann Kirkpatrick will challenge Republican Sen. John McCain, according to a source with knowledge of Kirkpatrick’s plans, giving Democrats a top recruit and a potential pickup opportunity.

Kirkpatrick made calls Monday to inform people of her plans, the source told CQ Roll Call. Her bid also opens up Arizona’s 1st District, a GOP-leaning seat spanning the northeast quadrant of the state.

An hour after this story was published, Kirkpatrick sent out an email making it official. “I love this state, and I’ve worked hard all my life to put Arizona first,” she said in a video. “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.”

She touted her service on the House Veterans’ Affairs Committee and work on a project she described as aimed at wildfire prevention and job creation in Arizona.

In the Senate contest, McCain, 78, is the heavy front-runner in his quest for a sixth term. But he faces a potentially strong challenge from the right flank of his party that could imperil his re-election bid, which had been rated a Republican Favored contest by the Rothenberg & Gonzales Political Report/Roll Call. The rating changed Tuesday to Leans Republican.

Kirkpatrick, 65, won re-election last fall in this district against all odds, defying a GOP wave that felled fellow moderate House Democrats. She has strong ties to the district’s Native American population, which made her uniquely able to carry the seat.

A case is also currently pending with the Supreme Court, which heard arguments earlier this year on whether the state’s congressional district lines — drawn by an independent redistricting commission —are unconstitutional. If the court throws out the current congressional map, Arizona’s districts are almost certain to become more favorable to Republicans, imperiling members such as Kirkpatrick.

Democratic operatives speculate that if the current congressional map is tossed by the court, fellow Democratic Rep. Kyrsten Sinema could also look at a Senate bid. Republicans would likely make her 9th District, located in the Phoenix suburbs, less competitive for the Democrats.

Sources with knowledge of Kirkpatrick’s plans said the congresswoman had long planned on running for Senate this cycle but wanted to announce before the Supreme Court’s decision, to avoid looking as if she were searching for a job if her 1st District became too Republican to carry.

Even if the district lines stay the same, Democrats will not have an easy time there. GOP presidential nominee Mitt Romney carried the 1st District by a 3-point margin in 2012, while McCain carried it by the same spread four years earlier. The Rothenberg & Gonzales Political Report/Roll Call on Tuesday changed the 1st District race rating to Tossup.

Rancher Gary Kiehne, who barely lost a GOP primary to the eventual Republican nominee, now-former state Speaker Andy Tobin, already announced a bid. Tobin, who lost to Kirkpatrick by a 5-point margin in the 2014 GOP wave, is also considering giving it another try.

Arizona GOP operatives listed a handful of others who could also wage bids.

They include:

• State Speaker David Gowan, who succeeded Tobin in that role, and had been contemplating a challenge to Kirkpatrick even before her Senate bid, according to a source with knowledge of his plans.
• Steve Pierce, the majority whip in the state Senate. GOP operatives say Pierce would be a top-tier candidate.
• David Tenney, the director of the Arizona Residential Utility Consumer Office, could also look to run. Republican operatives said Tenney, a former Navajo County supervisor, would also be a top-tier contender.
• Pinal County Sheriff Paul Babeu and Flagstaff City Councilman Jeff Oravits could also look to run, GOP operatives said.

Correction 1:30 p.m.

A previous version of this article misstated Pierce’s title in the Arizona Senate. He is majority whip.

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