Senate Democrats and supportive outside groups have built a massive cash advantage over Republicans 3½ months before the midterm elections, raising GOP concerns that they will squander a golden opportunity to grow their narrow majority.

All told, Democratic candidates in 10 of the most critical races are sitting on $75 million, while their Republican rivals hold $33 million in cash on hand, according to a review of campaign finance documents filed in recent days.

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The gaps are widest in some of the red states President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE carried by large margins in 2016.

In Missouri, Sen. Claire McCaskill Claire Conner McCaskillMomentum growing among Republicans for Supreme Court vote before Election Day Democratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally MORE (D) has $12 million on hand, four times the $3 million held by Attorney General Josh Hawley (R).

In West Virginia, Sen. Joe Manchin Joseph (Joe) ManchinManchin defends Supreme Court candidate Barrett: 'It's awful to bring in religion' The Hill's Morning Report - Sponsored by Facebook - Trump, GOP allies prepare for SCOTUS nomination this week Trump meets with potential Supreme Court pick Amy Coney Barrett at White House MORE (D) has $6.2 million in the bank, compared with just $895,000 for Attorney General Patrick Morrisey, who depleted his account in winning May’s Republican primary.

North Dakota Sen. Heidi Heitkamp Mary (Heidi) Kathryn HeitkampHarris faces pivotal moment with Supreme Court battle Centrists, progressives rally around Harris pick for VP 70 former senators propose bipartisan caucus for incumbents MORE (D) has twice the cash on hand as her rival, Rep. Kevin Cramer Kevin John CramerMomentum growing among Republicans for Supreme Court vote before Election Day On Paycheck Protection Program, streamlined forgiveness is key McConnell shores up GOP support for coronavirus package MORE, who joined the race in January.

In Florida, Sen. Bill Nelson Clarence (Bill) William NelsonDemocrats sound alarm on possible election chaos Trump, facing trouble in Florida, goes all in NASA names DC headquarters after agency's first Black female engineer Mary W. Jackson MORE (D) holds what appears to be a commanding cash lead over Gov. Rick Scott (R), $13.7 million to $4.5 million.

But Scott, who spent tens of millions of dollars on his campaigns for governor, has already spent freely on this race and raised more than $10 million in his first quarter as a candidate.

In Indiana, Sen. Joe Donnelly Joseph (Joe) Simon DonnellyHarris faces pivotal moment with Supreme Court battle Trump meets with potential Supreme Court pick Amy Coney Barrett at White House Names to watch as Trump picks Ginsburg replacement on Supreme Court MORE (D) holds a massive $6.4 million to $1 million lead over former state legislator Mike Braun (R), though Braun has indicated he, too, will pour millions into his own coffers.

In states where Republicans are playing defense, there is more reason for optimism.

Though she faces a competitive primary, Arizona Rep. Martha McSally Martha Elizabeth McSallyThe Hill's Campaign Report: Presidential polls tighten weeks out from Election Day Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' New ABC/WaPost poll finds Trump edging Biden in Arizona, Florida MORE (R) has kept pace with her likely Democratic rival, Rep. Kyrsten Sinema, who holds just an $800,000 cash edge.

In Nevada, Sen. Dean Heller Dean Arthur HellerOn The Trail: Democrats plan to hammer Trump on Social Security, Medicare Lobbying World Democrats spend big to put Senate in play MORE (R) has a $2 million advantage over Rep. Jacky Rosen Jacklyn (Jacky) Sheryl RosenHillicon Valley: Election officials prepare for new Russian interference battle | 'Markeyverse' of online fans helps take down a Kennedy | GOP senators unveil bill to update tech liability protections Google, Apple, eBay to meet virtually with lawmakers for tech group's annual fly-in Senate Democrats demand answers on migrant child trafficking during pandemic MORE (D), though Rosen has raised more than Heller in four straight quarters.

And in Tennessee, Rep. Marsha Blackburn Marsha BlackburnTaylor Swift on National Voter Registration Day: 'We need everyone' Democrats smell blood with new DHS whistleblower complaint Hillicon Valley: Election officials prepare for new Russian interference battle | 'Markeyverse' of online fans helps take down a Kennedy | GOP senators unveil bill to update tech liability protections MORE (R) has double the money that former Gov. Phil Bredesen (D) holds in reserve, $7.3 million to $3.6 million — though Bredesen has spent freely of his fortune to fund an early onslaught of television ads.

Along with those eight states, The Hill included in its analysis Michigan and Pennsylvania, where Democratic incumbents are favored in states won by Trump.

Democrats would need to net two Senate seats to win back the majority.

In Montana, where the most recent fundraising reports are not available, Sen. Jon Tester Jonathan (Jon) TesterDemocrats shoot down talk of expanding Supreme Court Pence seeks to boost Daines in critical Montana Senate race This World Suicide Prevention Day, let's recommit to protecting the lives of our veterans MORE (D) has $6.1 million on hand, far more than state Auditor Matt Rosendale (R), who spent big to beat two fellow Republicans in a primary last month.

Other potentially competitive states are falling off the map as Democrats build big cushions over their GOP rivals. Sens. Sherrod Brown Sherrod Campbell BrownHarris faces pivotal moment with Supreme Court battle Remote work poses state tax challenges Senate Democrats release report alleging Trump admin undermined fair housing policies MORE (D-Ohio), Bob Casey Robert (Bob) Patrick CaseySecond GOP senator to quarantine after exposure to coronavirus GAO report finds brokers offered false info on coverage for pre-existing conditions Catholic group launches .7M campaign against Biden targeting swing-state voters MORE Jr. (D-Pa.) and Tammy Baldwin Tammy Suzanne BaldwinSenators introduce bipartisan bill to mandate digital apps disclose country of origin Keep teachers in the classroom Cher raised million for Biden campaign at LGBTQ-themed fundraiser MORE (D-Wis.) all have huge advantages, putting states that might have been in play outside the GOP’s reach.

“Strategically speaking, we should be looking at a broader playing field of races than I think people are right now, because the financial concerns are constraining the map,” said Brian Walsh, a Republican strategist close to Trump who is closely tracking the midterm campaign.

The discrepancy is as significant among prominent outside groups that will spend tens of millions of dollars in the battle for the Senate.

The Democratic Senatorial Campaign Committee had about twice as much cash on hand, $34 million, as the National Republican Senatorial Committee (NRSC), $16 million, through the end of May, the last date for which disclosure reports are available.

The Senate Majority PAC, the largest Democratic super PAC, has more than twice as much in the bank, $29 million, as the $13.5 million held by the Senate Leadership Fund, its Republican counterpart.

“We’re in a moment, and fundraising is certainly fluid and we have a long way to go, but Democrats have certainly been engaged in this cycle and are eager to see a change in the U.S. Senate,” said J.B. Poersch, who heads the Senate Majority PAC.

With months to go, the overall Democratic fundraising edge may not hold. Two years ago, Democrats held a similar edge until a wave of late Republican money helped even the playing field. But an early cash advantage for one candidate can dissuade an outside group backing the other candidate from committing funds to what looks like an unwinnable race. If a race appears competitive, outside groups will turn a financial disparity into parity.

“We have these types of conversations every two years, and it is hard to look back and find many races where money was the decisive factor,” said Rob Jesmer, who ran the NRSC for two election cycles.

Some Republicans suggested the outside groups have been slower to raise big money in part because of intraparty competition from super PACs tasked with keeping control of the House. The Congressional Leadership Fund, closely tied to Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.), has pulled in huge contributions from mega-donors like Sheldon Adelson, who worry more about losing the House than they do losing the Senate.

“Donors tend to gravitate towards whatever they feel is more prominent, and right now concerns about losing the House outweigh concerns about losing the Senate,” Walsh said. “The concern about the House is real, and justifiably so.”

But there is still plenty of money awash in the battle for the Senate. Candidates and their affiliated outside groups have purchased or reserved more than $270 million in television advertising in just 11 states with Senate races this year, according to two sources watching the advertising market.

In those states — Arizona, Florida, Indiana, Missouri, Montana, North Dakota, Nevada, Ohio, Tennessee, West Virginia and Wisconsin — Democrats have reserved $152 million in airtime, compared with $118 million blocked off by Republicans.

The two sides have purchased or reserved more than $63 million in Florida, $40 million in Missouri, $44 million in Nevada, $30 million in Indiana and $21 million in Arizona, according to the sources.

Several senators, including Baldwin, Heitkamp, Brown, Tester and Donnelly, have spent weeks airing commercials. In Tennessee, Bredesen, running for an open seat held by retiring Sen. Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump MORE (R), began advertising in March.

Among Republican challengers, only one — Florida’s Scott — has run more general election-focused advertising than his Democratic opponent.