WASHINGTON — GOP contenders who were lagging behind their Democratic rivals in campaign fundraising are poised to see a cash infusion thanks to a Supreme Court ruling Tuesday that will allow Republicans to buy up airspace at discounted rates in the lead-up to the 2026 midterms.

The Supreme Court’s decision allowing coordinated spending between political parties and candidates delivered a blow to Democrats, members of both parties agreed, as the GOP’s best outcome would be flipping three Senate seats and winning more than a dozen House seats to increase control of Congress.

“The Supreme Court’s decision is a major setback for the Democrats’ viral fundraisers in states like Texas and Maine,” Sean Cooksey, managing director at BGR Group and former chairman of the Federal Election Commission, told The Post.

“What would have been a significant financial advantage over their Republican opponents will be neutralized by the RNC’s war chest and its new ability to coordinate ads with candidates,” added Cooksey, who most recently served as counsel to Vice President JD Vance.

Senate Republicans are hoping to regain control of Michigan, New Hampshire and Georgia, while retaining seats in Iowa, Alaska, Ohio, North Carolina and Maine. The House GOP’s main campaign arm is also eyeing around three dozen vulnerable Dem seats.

“The map is much smaller this go around than it has been in past midterms,” a Republican National Committee official said. “That makes our money go a lot further than it has in past midterms.”

The Republican National Committee already boasts a whopping $125 million campaign war chest, compared with the Democratic National Committee’s more than $14 million — on top of another $18 million in debt.

And the high court’s ruling will let the RNC, in addition to the GOP’s top two congressional campaign committees, make good use of that cash on hand for campaign advertising in contests where Democrats had been betting on candidates with large national profiles, according to party insiders.

Maine Senate Democratic candidate Graham Platner, for instance, has far surpassed incumbent GOP Sen. Susan Collins’s fundraising, with more than $16 million raised and $2 million cash on hand. Collins recorded just a little more than $310,000 cash on hand in her latest quarterly filing.

In Texas, Senate Democratic hopeful James Talarico has raised more than $40 million and recorded nearly $10 million cash on hand in his race against state attorney general Ken Paxton, who has just over $2 million in his campaign war chest and has raised more than $7.5 million, per the latest campaign finance filings.

“We’re still in primary season,” the RNC official noted. “Seeing who our opponents are gonna be matters a lot.”

“Even for a lot of the talk recently following New York, Colorado,” the official added, referencing primary races where left-wing challengers beat Democratic incumbents, “the crazy rhetoric and ideas … despite all that, obviously, what they’re selling is very exciting to a portion of their base.”

For that reason, Democrats’ favored candidates have run higher fundraising figures for their committees, while their party’s committees are being beaten in contributions by the GOP’s major political committees.

Typically, Democrats have been able to use the fundraising advantage from individual candidates to buy ads at cheaper rates, the National Republican Senatorial Committee (NRSC) noted in a Tuesday memo, but that rate, known as the Lowest Unit Charge, will now be available to party committees.

Another GOP operative added that the coordinated spending will mean that committees no longer will be making public announcements of cash reservations, giving the party a tactical edge in where they decide to send funding.

“The NRSC can spend without limit in direct coordination with all Senate campaigns on all expenditures,” the memo stated.

“Historically, most NRSC advertising was produced and distributed independently — it could not be informed by strategic conversations with the campaign about message, targeting, timing, or creative. Those restrictions are now gone.”

In April, for instance, Senate Republicans’ top super PAC, the Senate Leadership Fund, announced $236 million in ad reservations for incumbents running in Maine, North Carolina, Ohio, Iowa and Alaska as well as challengers to Dem incumbents in New Hampshire, Georgia and Michigan.

Previously, the FEC capped spending to Senate candidates’ campaigns at around $4 million and House campaigns at around $65,000.

DNC chair Ken Martin and other party committee leaders — including DSCC Chairwoman and Sen. Kirsten Gillibrand (D-NY) as well as DCCC Chairwoman and Rep. Suzan DelBene (D-Wash.) — slammed the decision as “a win for billionaire donors and special interests who want more influence over the GOP agenda and an invitation for corruption.”

Democratic sources added that the court win wouldn’t have been as much of a blow had the DNC been keeping up with the RNC’s fundraising totals since the 2024 election.

“You’d be really hard pressed to make the case for how they can be a really effective outfit for 2026,” the RNC official also said.

The Supreme Court ruling in NRSC v. Federal Election Commission (FEC) came after the main campaign arm for the Senate GOP filed a challenge to the Federal Election Campaign Act of 1971, alleging it violated the First Amendment by capping coordinated spending, which is mainly used on campaign advertising.

It’s considered the biggest decision on US campaign finance since the 2010 Citizens United ruling that allowed corporations to donate without limits to super PACs.