Two groups affiliated with American Crossroads – the decade-old powerful outside group that supports Republican candidates and causes – are spending big bucks on TV commercials in a key Senate race in Georgia, a once reliably red state that recent polling indicates is now up for grabs.

Fox News has learned that One Nation – the nonprofit advocacy arm of American Crossroads – on Wednesday is placing an $8.65 million ad buy to run spots for four weeks in Georgia, starting on August 4.

And Senate Leadership Fund -- a Crossroads-affiliated super PAC that works to “protect and expand” the GOP majority in the Senate – is expected later this week to shell out up to $13.5 million to start running ads in mid-September.

REPUBLICANS RETURNING FIRE IN BATTLE FOR CONTROL OF THE SENATE

The ad buys -- the latest by Republican groups in recent weeks -- illustrate that Georgia is increasingly becoming a battleground state. The National Republican Senatorial Committee, the reelection arm of Senate Republicans, booked at least $2 million to run spots in the state starting later this month, as per the ad-tracking firm Advertising Analytics. And President Trump’s reelection campaign reserved air time to run commercials in Georgia from September through Election Day.

“The far-left has made no secret of their ambitions of flipping Georgia to muscle their radical agenda through the Senate. We’re not going to let that happen,” Senate Leadership Fund and One Nation President Steven Law told Fox News.

Republicans are working to hold their 53-47 majority in the Senate. They’re defending 23 of the 35 seats up for grabs in November. While more than half a dozen GOP incumbents are facing challenging reelections, only one or two Democratic senators are considered vulnerable.

Republicans are hoping to turn the tide – or least try to level the playing field – in a Senate cycle that’s seen them outspent. Democrats have been riding a wave of momentum, thanks to very strong fundraising and successful recruits.

There are two Senate elections in Georgia in November. GOP incumbent Sen. David Perdue -- who’s running for reelection to a second, six-year term – is facing a serious challenge from Democrat Jon Ossoff, who narrowly lost a 2017 special congressional election that was the most expensive House election in history.

The commercials by One Nation and Senate Leadership Fund are for the Purdue-Ossoff race.

FOX NEWS POLL SHOWS CLOSE PRESIDENTIAL AND SENATE RACES IN GEORGIA

The most recent Fox News poll in Georgia – conducted June 20-23 – showed Purdue with a narrow 45-42 percent edge over Ossoff. That same survey indicated an extremely close contest between President Trump and Democratic challenger Joe Biden in the White House race.

There’s also a special Senate election on November 3 in the race to fill the final two years of the term of former Republican Sen. John Isakson, who stepped down in December due to health reasons.

GOP Gov. Brian Kemp named Republican Kelly Loeffler as Isakson’s temporary replacement. She’s running in the November election to fill the rest of Isakson’s term. So is Republican Rep. Doug Collins, who President Trump had hoped would be appointed as Isakson’s temporary replacement. A number of Democrats are also running.

If no candidate tops 50 percent in the special election, a runoff contest between the top two finishers will be held on January 5.