Republican groups poured over $740 million into congressional races between Labor Day and mid-October, yet polling in competitive Senate races has barely shifted and Democrats remain favored to flip the House, according to a CNBC analysis of campaign spending data and election forecasts.

The GOP entered the final stretch with roughly $1 billion available across major organizations, nearly double the $579 million available to comparable Democratic groups. Elon Musk added $276 million to Republican coffers since July, making him the cycle's largest known donor with $366 million total. Nine of the top 10 donor groups are Republican-aligned, accounting for 86 cents of every dollar from the biggest contributors.

Yet in nine competitive Senate races tracked by the Cook Political Report, Democrats lead in polling averages across Alaska, Georgia, Iowa, Kansas, Maine, Michigan, Minnesota, New Hampshire, North Carolina, Ohio and Texas, showing little movement from before the spending surge. Republican operatives and election observers told CNBC the money has not produced expected shifts in voter sentiment.

Neil Newhouse, partner at Republican polling firm Public Opinion Strategies, said: "Money is an amplifier, not a magic wand. You can buy all the airtime in the world, but if the political climate is blowing 30 miles an hour in your face, ad volume alone isn't going to turn the weather around."

The spending disadvantage is steeper than raw dollar totals suggest. Federal law entitles candidates to broadcasters' lowest unit rate in the final 60 days before an election, but outside super PACs receive no such protection. As a result, GOP super PACs pay three times more per viewer than Democratic campaigns can in some markets. In Dallas, Democrat James Talarico's $2.4 million campaign buy generated 48 average views per voter; the pro-Ken Paxton super PAC spent $7.8 million for roughly 81 views, according to AdImpact data analyzed by CNBC.

Across nine key Senate races through September 30, Republicans led broadcast TV spending in seven and outspent Democrats by 26% overall yet generated only 7% more airings. Broadcast TV accounts for 48% of projected political spending in the 2026 cycle.

Despite $113 million in negative advertising targeting Texas Democrat James Talarico since the primary, a Siena College poll released Tuesday showed Talarico leading Republican Ken Paxton 48% to 44%, down only slightly from a six-point lead in September.