ATLANTA, GA - MAY 24: During the Georgia primary election, a voter checks his printed ballot at the Park Tavern polling location on May 24, 2022 in Atlanta, Georgia. Voters across Georgia will be voting on several positions, including U.S. Senate seats, Georgia Secretary of State, and the Governor position.  (Photo by Jessica McGowan/Getty Images)
Will Democrats hold on to the Senate?
05:40 - Source: CNN
CNN  — 

After being outspent by Democrats all summer, supporters of Republican candidates in the 10 most competitive Senate races have dumped more than $365 million on TV and digital ads since the beginning of September to catch up.

That financial gap is being filled by the Senate Leadership Fund, a super PAC affiliated with Republican Senate Minority Leader Mitch McConnell, according to data from AdImpact, an advertising tracking firm. With more than $196 million invested on the airwaves and online so far, the Senate Leadership Fund is by far the largest TV and digital advertiser this fall in six of the 10 states deemed most likely to flip by CNN — Georgia, Nevada, New Hampshire, North Carolina, Ohio and Wisconsin.

It’s hard to overstate the effect the super PAC has single-handedly made on advertising in the final two months of the elections. With its help, Republicans are outspending their Democratic rivals on ads in four of those 10 competitive races. But if not for the Senate Leadership Fund, Democrats would command the ad markets in every race but Florida, the most red-leaning of the 10 states. The Senate Leadership Fund has not spent any money on ads this fall for Florida Republican Sen. Marco Rubio.

An advantage in ad spending, simply put, means more visibility for that candidate, whether voters see them on TV or online. “We operate under the mindset that you never want to give up ground to your opponent,” said Eric Wilson, a political technologist who led the digital team for Rubio’s 2016 presidential campaign. “So if your voters are hearing something negative about you, you want to make sure that they’re also hearing something positive.”

The stakes for both parties are incredibly high. With the Senate currently split 50-50, both parties need every seat possible to win control of the majority, said Nathan Gonzales, the editor of Inside Elections and a CNN contributor. Inside Elections currently projects three scenarios for the Senate in November: Republicans gain one seat, Democrats gain one seat, or that the chamber will remain divided with Vice President Kamala Harris serving as the tie-breaking vote to keep Democrats in the majority.

“The fight for the Senate is so close that neither party can afford to have any mistakes,” Gonzales said.

In states with open races, such as Pennsylvania and Ohio, the Republican candidates emerged during the summer from competitive and expensive primaries without a lot of infrastructure or money left over for the general election. “SLF has had to try to fill in the gap and pick up the slack,” Gonzales said.

Some of the Republican nominees also lack campaign experience and especially stand to benefit from the extra financial boost. The Republican candidates in Arizona, Georgia, Ohio and Pennsylvania — Blake Masters, Herschel Walker, JD Vance and Dr. Mehmet Oz, respectively — have never run for public office.

“In some of the Senate races, especially where you have these novice candidates, I think they’ve struggled just to figure out exactly how to run a campaign,” said Alan Abramowitz, a political scientist at Emory University. The wide availability of outside money means organizations like the Senate Leadership Fund can afford to come in and run rescue operations, Abramowitz said.

CNN reached out to the Senate Leadership Fund for comment and was directed to its website’s About page. “As an independent Super PAC, the Senate Leadership Fund has one goal,” the webpage says. “To build a Republican Senate majority that will defend America from Chuck Schumer (D-NY) and Senate Democrats’ destructive far-left agenda.”

That goal to recapture the Senate reveals the fault lines within the GOP. In a likely attempt to appeal to former President Donald Trump, the Republican candidates from Pennsylvania, Arizona, New Hampshire and Ohio have refused to say they support McConnell becoming the majority leader should their party regain the Senate. Trump has endorsed the candidates in all four states, and the SLF is the top Republican advertiser in Pennsylvania, New Hampshire and Ohio.

But the GOP’s super PAC spending masks a larger problem for Republican Senate candidates, experts told CNN: A lack of campaign infrastructure.

“The Democrats have consistently done a better job investing in campaign infrastructure, whether that’s organizing volunteers, mission specific groups or digital infrastructure,” Wilson said. “Republicans are really just focused on, ‘Let’s spend as much money as we can in the final stretch and win it that way.’”

Although the Democrats are no strangers to super PACs — the Chuck Schumer-affiliated Senate Majority PAC is the second-largest advertiser in the last two months of the election after the SLF — Democratic candidates are spending more on ads from their own campaigns. In nine of the 10 competitive races, the Democratic Senate candidates’ campaigns are funding roughly a third or more of their ads.

“Republicans are trying to defeat some of the most well-funded candidates in the Democratic Party,” Gonzales said, such as Mark Kelly (D-AZ) and Raphael Warnock (D-GA). Kelly and associated groups have spent $53.4 million on ads for the fall, with nearly $23 million of that spent by his own campaign. Ads for Masters currently total $20.9 million.

Support from both individual donors and multiple outside groups provides a financial security blanket not available for candidates who rely on one deep-pocketed super PAC, such as the SLF — and are at a higher risk of falling out of its favor. In late September, for example, the SLF pulled more than $9 million worth of ads for Masters around the same time a Marist poll showed Kelly leading by 10 percentage points in Arizona. The super PAC has now contributed less than 3% of the ad spending for Masters, whose own campaign has spent roughly $1.4 million on advertising.

“If you’re relying on outside support, you have less control over the when and what an outside group will do,” Gonzales said. “There might be the perception that outside groups have an unlimited amount of resources, but every group has limited dollars and they’re gonna spend where they think is necessary to get control.”

But having to rely on outside money doesn’t mean any of the Republican candidates still can’t win. Inside Elections ranks three of the 10 races as toss-ups, and four others with a Republican advantage. In a midterm election year with a Democratic president who is somewhat unpopular, the national political environment is still very favorable for Republicans, Abramowitz said.

CNN’s David Wright contributed to this report