WASHINGTON — (CNN) A major super PAC associated with House Republican leaders announced Monday a $10 million expenditure to boost vulnerable House GOP candidates as it works to maintain control of the chamber.

The move comes as Republican Party officials wrestle with how to allocate precious financial resources between Donald Trump’s faltering presidential campaign and House and Senate races party leaders see as must-win if they are forced to keep in check a Hillary Clinton presidency.

The Congressional Leadership Fund’s spending on TV and digital advertising — as well as get-out-the-vote efforts — is aimed at 12 of the most competitive seats this fall that could determine if Democrats can make up the 30-seat deficit they face now and reclaim the majority after six years out of power.

The critical late-stage campaign advertising will run in mid- and late October, the group said.

“This is the first wave of efficient, strategic ad reservations,” said Mike Shields, a longtime House leadership aide and Republican Party official who leads the group.

The largest chuck of the money — $1.7 million — will go for TV advertising in the South Florida district of Rep. Carlos Curbelo, an endangered first-term lawmaker who was an early GOP critic of Trump.

The PAC also will spend $3.4 million for three Democratic seats they hope to pick up — the Sacramento, California, seat of Rep. Ami Bera, the Omaha, Nebraska, seat of Rep. Brad Ashford, and the open Florida seat being vacated by Rep. Patrick Murphy, who is running for Senate.

The other seats targeted are in New York, Texas, Wisconsin and Iowa.

“We will continue to add to these buys in the coming weeks, including more television advertising, digital advertising and further ground troop investments,” Shields said.

“Our historically strong fundraising has put us in a position to not only protect Republicans in tough races, but also to take the fight to Democrats on their turf.”

Despite Trump’s recent sagging polls, many Republicans remain confident they will not suffer serious down ballot losses and will hold the House and Senate.

They point to internal polling that shows House Republicans maintaining their advantages.

“Donald Trump is supposed to be an anvil around the neck of Republican candidates down-ballot and around the country, but up to this point in the cycle, vulnerable GOP incumbents are holding their own,” said Nathan Gonzalez, who studies House races for the non-partisan Rothenberg and Gonzales Report.

But news of the expenditure triggered an emailed fundraising appeal from the Democratic Congressional Campaign Committee under the headline: “Paul Ryan TERRIFIED,” suggesting the spending is a reflection the speaker is afraid he will lose his gavel in November.