PHOENIX-- Arizona Rep. Martha McSally has told Republican colleagues that she will enter the race for the U.S. Senate seat being vacated by fellow Republican Jeff Flake, a move that puts a mainstream candidate who could win backing from President Donald Trump into the primary race.

McSally hasn't made a formal announcement of her intention to run in next year's Republican primary. But Arizona Rep. David Schweikert said Tuesday that she told fellow Arizona GOP members of Congress that she was running.

"She said she's in for Senate," Schweikert said of the talk he had with the southern Arizona congresswoman on Monday. "It was one of those just sort of as you're running around from votes, so there wasn't much of a conversation on my part."

McSally's staff didn't immediately respond to requests for comment.

A former Air Force fighter pilot who represents a moderate district, McSally would face off against former state Sen. Kelli Ward and could face other Republicans who have been considering getting into the race.

Ward lost badly in a challenge to Sen. John McCain last year but has been gaining traction in the Senate race and became the instant front-runner when Flake backed out.

Democratic Rep. Kyrsten Sinema is seeking her party's nomination along with several lesser-known Democrats.

Flake announced last month that he would not seek re-election. He has been an outspoken critic of President Donald Trump and acknowledged that he could not win a GOP primary in the current political climate.

Mainstream Republicans in Arizona have been searching for another primary candidate because they believe Ward cannot beat Sinema.

Ward discounts talk that she's unelectable, saying in a recent interview that people are rallying behind her.

"The people who are dismissive, some of them have sour grapes because they didn't get in at the right time to be able to build the organization that I've built," she said.

Even ahead of an expected McSally announcement, she was targeted by conservative groups. A group affiliated with former Trump strategist Steve Bannon launched a website last week attacking what it called "McSally's troubling history of supporting amnesty and being weak on illegal immigration."

If McSally formally enters the race, it could make it easier for Democrats to retake her seat representing Arizona's 2nd District.

The seat had been held by former Rep. Gabby Giffords, then won by Democrat Ron Barber when she stepped down in 2012 following an assassination attempt that left her badly injured. McSally defeated Barber by 167 votes when he sought re-election in 2014.

She handily won re-election last year by a 14 percentage point margin.

A House re-election may be tougher next year, with former U.S. Rep. Ann Kirkpatrick seeking her party's nomination.

McSally has threaded a needle in her Tucson-area district, pushing border security and veterans issues while fighting to save the jet she flew in combat, the A-10, from retirement by the Air Force.

In May, she was quoted using an expletive urging fellow Republicans to repeal the Affordable Care Act in advance of a vote. She took heat back in her district for the vote and has worked since then to moderate her stance.