Can $1 billion power the GOP to victory in the midterms? Some campaigns fear it's too late

WASHINGTON (AP) — Republicans are entering the final month of the midterm campaign increasingly anxious that the $1 billion at their disposal may not be enough to fend off sweeping losses as the party reckons with President Donald Trump's unpopularity, persistent cost concerns and the fallout from the war in Iran.

The cash advantage, spread out across a half-dozen groups, is driven largely by the Trump-aligned MAGA Inc., which had nearly $416 million in cash on hand at the end of August and began stepping up its spending on critical races in September.

WATCH: Who's spending big, and where, in most expensive election cycle ever

But that money may have come too late, forcing the president's group to pay much higher rates because of the shrinking availability of air time. Four Republican Senate campaign officials said groups that reserved advertising time last spring paid much lower rates than MAGA Inc. and its affiliated groups.

Instead, by waiting until September, Trump-connected organizations are sometimes paying more than five times what they would have spent if they acted earlier.

A representative of MAGA Inc. familiar with the group's strategy said its spending has allowed Republicans to keep races more competitive than they would have been otherwise. In some cases, the group has been the only one on the air criticizing Democratic candidates.

The MAGA Inc. representative and the Republican Senate campaign officials spoke on condition of anonymity to discuss internal strategy.

The challenge is acute in places like Texas, where Trump traveled on Wednesday for the second time in a week to stump for Republican Ken Paxton's Senate campaign. The state hasn't elected a Democratic senator since 1988, yet MAGA Inc. has spent more than $22 million in the past month, according to the ad tracking firm AdImpact.

WATCH: Trump speaks at rally for Senate candidate Ken Paxton in San Antonio

Another group, Texas PAC, which is aligned with Senate Majority Leader John Thune, has spent more than $83 million on advertising in the past month, an extraordinary amount to protect what's normally a safe Republican seat.

One of those advertisements, which featured Paxton's estranged wife saying she's supporting the full Republican ticket, aired across the United States last weekend during a football game between the Dallas Cowboys and the Houston Texans.

Candidates are charged a lower advertising rate than outside groups, so the late infusion of super PAC cash has come at a steep price.

MAGA Inc., which is running ads primarily on streaming services, has been charged roughly $894 per airing, according to AdImpact, while Texas PAC has been charged roughly $809 for a mix of broadcast and streaming. That compares with about $290 for Democratic nominee James Talarico's campaign, also on broadcast and streaming.

Those averages mask some of the more glaring disparities. For example, during a football game last month, Texas PAC was charged $450,000 to air a single spot in the Austin market. Talarico's campaign paid $50,000 for a spot during the same game in the same market, according to AdImpact.