The super PAC backing Tim Scott's presidential campaign is canceling its slate of upcoming television ads, according to a memo sent to donors obtained by CNN, as the South Carolina senator's candidacy struggles to gain traction in the 2024 Republican primary.

Trust in the Mission PAC is pulling the plug on the remainder of its $40 million TV and digital ad reservation first made in July, citing a "stuck" primary field dominated by former President Donald Trump, PAC co-chair Rob Collins wrote in the memo, which was first reported by Politico.

"The Fall Republican primary is stuck," Collins said. "Donald Trump leads a cluster of statistically tied contenders by a wide margin. Vote share of non-Trump candidates trades up and down, but no campaign has achieved break away velocity. The fundamentals of this race remain unchanged: President Donald Trump occupies a lane to himself."

Collins added, "So, we are doing what would be obvious in the business world but will mystify politicos -- we aren't going to waste our money when the electorate isn't focused or ready for a Trump alternative. We have done the research. We have studied the focus groups. We have been following Tim on the trail. This electorate is locked up and money spent on mass media isn't going to change minds until we get a lot closer to voting."

The super PAC will continue to spend money on organizing, fundraising, and hosting events -- including with Scott as a "special guest" of events hosted by the group, Collins said in the memo, replicating a tactic used by the super PAC supporting Florida Gov. Ron DeSantis' campaign.

Collins said the shift in strategy will help support Scott as he looks to increase his appeal in early state nominating contests, with Iowa being a particular focus.

"We believe that shifting from a media-centric to a grassroots-focused approach is the best use of our money. This enables us to leverage our greatest asset, Tim Scott himself," Collins wrote in the memo. "Offering Tim Scott the chance to interact with as many voters as possible as a guest at TIM PAC events across the Hawkeye State will help his campaign build standing with caucus-goers."

The PAC's canceling of media reservations comes as Scott's campaign struggles to break through as a viable alternative to Trump. A Fox News poll released last week found Scott with 1% support nationally among GOP primary voters. Scott has not yet qualified for the third Republican presidential debate in November.

Scott's campaign is also burning through a once-formidable cash reserve, according to new campaign finance filings. The campaign raised nearly $4.6 million in the third fundraising quarter, but spent $12.4 million, lessening a stockpile he had transferred from his Senate campaign when he launched his presidential bid earlier this year.