Senate Minority Leader Chuck Schumer Chuck SchumerVideo of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral Graham signals support for confirming a Supreme Court nominee this year Pelosi orders Capitol flags at half-staff to honor Ginsburg MORE (D-N.Y.) phoned Rep. Kyrsten Sinema (D-Ariz.) during the August recess and told her he would back her over other primary candidates should she decide to run against vulnerable Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (R-Ariz.), multiple sources told The Hill.

Schumer also placed a phone call with Phoenix Mayor Greg Stanton, another Democrat who had been eyeing a Senate bid, and told him he was going with Sinema, the sources said.

The phone calls are the clearest sign yet that Sinema, 41, a centrist Democrat serving her third term in the House, is gearing up for a Senate run in the Grand Canyon State.

An announcement is expected any day.

It’s not even certain that Sinema would face her former House colleague, Flake, in a general-election match-up. He’s deeply unpopular in Arizona and has been locked in a months-long feud with President Trump, whose allies are working to unseat Flake for his disloyalty.

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A HighGround poll in Arizona found that one Trump-inspired GOP primary challenger, former state Sen. Kelli Ward, is leading Flake 43 percent to 28 percent. That same poll showed Sinema beating Flake in a potential match-up 41 percent to 33 percent.

“She’s done a very effective job working across the aisle. And she voted against Nancy Pelosi twice for Speaker,” said former Rep. Matt Salmon Matthew (Matt) James SalmonCOVID-19's class divide creates new political risks Arizona voters like Kyl but few think he'll stick around Former Sen. Jon Kyl to replace McCain in Senate MORE (R-Ariz.), whom conservative groups have unsuccessfully tried to recruit to challenge Flake in a primary.

“I think she will be a formidable challenger to whoever she runs against,” Salmon said.

Spokespeople for Sinema, Stanton and Schumer all declined to comment for this story. Schumer’s blessing essentially clears the path for Sinema and means she would have access to staffing and other resources from the Senate Democrats’ campaign arm, the Democratic Senatorial Campaign Committee, which Schumer once led.

Stanton, who is in his second term as Phoenix mayor, is also eyeing Sinema’s House seat. But because hers is a swing-district seat, candidates from both parties will be lining up to run.