Congressional Democrats are whipping their GOP counterparts in fundraising heading into the 2018 elections, a key sign that a wave election may be building.

In both the Senate and House, Democrats are pulling money hand-over-fist in many of their most important races, according to campaign finance reports recently filed with the Federal Election Commission. Many Republicans are struggling to keep up — including some key incumbents in both chambers.

That trend is causing heartburn for many Republicans, who worry their chances of losing the House are growing due to President Trump’s unpopularity and Republican voters’ frustration with their failure to pass major legislation.

“It’s a serious problem,” former National Republican Congressional Committee Chairman Tom Cole (R-OK) told TPM. “It’s a very rough cycle coming up. Nobody’s had a good off year since 2002 and anybody that thinks the majority is not at risk or that they can’t be beaten is kidding themselves.”

The chances they could lose the Senate too are looking less like an impossibility even though Democrats are defending many more vulnerable seats. Republican senators warn that they better get tax reform done to please their donors and base or face an even bleaker scenario following their failure to repeal Obamacare.

“There is a warning that comes from lack of fundraising success, and it indicates that your agenda or your lack of accomplishment is something people are deciding is a problem as they make a decision about contributing to a campaign,” former National Republican Senatorial Committee Chairman Jerry Moran (R-KS) told TPM. “The fact that the fundraising is what it is is certainly not a positive, but it doesn’t mean that it’s ultimately a problem. There’s time to recover from the circumstance of low numbers now.”

Nine of the 10 Democratic senators from states President Trump won raised more than $1 million in the last fundraising quarter, easily outpacing most of their rivals. All 10 have at least $3 million stashed away, and seven of them have more than $5 million cash on hand.

On the flip side, the few Senate Republicans who might face real challenges posted less-than impressive hauls. Sen. Dean Heller (R-NV) was out-raised by his likely Democratic opponent, Rep. Jacky Rosen (D-NV). Sen. Jeff Flake’s (R-AZ) decision to retire came after he was out-raised by Rep. Kyrsten Sinema (D-AZ), who begins the Arizona Senate race with a big cash advantage over any of her likely opponents with $4.2 million in the bank.

Senate GOP challengers also struggled with fundraising. Only two Senate Republican candidates raised even half as much as the Democratic senator they’re hoping to take out next fall — Rep. Luke Messer (R-IN) and West Virginia Attorney General Patrick Morrissey (R). Like many other Republican Senate candidates, they’ll have to spend much of that money to win primaries.

Democrats even raised more than their GOP opponents in long-shot races. Democrat Doug Jones brought in more and had more money in the bank than former Judge Roy Moore (R) in Alabama ahead of their Dec. 12 special election, and Rep. Beto O’Rourke (D-TX) out-raised Sen. Ted Cruz (R-TX), though Cruz still has much more cash on hand.

Democrats aren’t counting their chickens yet — but they admit things seem to be going their way.

“This has been an amazing year. I’ve never seen anything like it,” Sen. Claire McCaskill (D-MO), who raised $2.7 million and has $7.1 million in the bank, told TPM.

“Our members are putting themselves in a strong position and we’re really seeing an increase in grassroots support and fundraising, lots of small-dollar contributions, which is a sign of increased political energy around the country,” Democratic Senatorial Campaign Committee Chairman Chris Van Hollen (D-MD) told TPM. “If this becomes part of a larger wave that’d be great, but we’re not banking on a wave. … We’re feeling like things are going as well as they can politically for our senators.”

The House side is even more promising for Democrats in their uphill fight to win back a chamber of Congress next year.

More than 30 incumbent Republicans raised less money than their Democratic challengers from July through September — an occurrence that’s almost unheard of this early in the election cycle — including vulnerable members like Reps. John Culberson (R-TX), Mimi Walters (R-CA) and Steve Knight (R-CA).

Some incumbent Republicans in tough seats posted huge fundraising numbers — Reps. Barbara Comstock (R-VA), Martha McSally (R-AZ) and Carlos Curbelo (R-FL) all had solid hauls — and many of the top-performing Democrats are going to have to spend big chunks of their war chests to win primaries, draining resources.

“It will be fun watching Democratic candidates bleed their campaigns dry on futile a mission to bolster their progressive bona fides,” said NRCC spokesman Jesse Hunt.

But it’s clear whose side has the energy — and big early fundraising is often an early sign of a party’s success in future elections.

The Democratic Congressional Campaign Committee and Democratic Senatorial Campaign Committee also out-raised their GOP counterparts once again, a pattern that’s held for most of this year, though the DSCC and NRSC have about the same cash on hand and the NRCC has more in the bank than the DCCC.

One big exception to this pattern: The Republican National Committee is wiping the floor with the Democratic National Committee, a major concern for Democrats as they head into a crucial midterm year. The RNC has $44 million in the bank to the DNC’s paltry $7 million.

The DNC is still recovering from a longterm fracture driven by years of neglect, information exposed by the Russian hacks, and distrust between the Bernie Sanders, Barack Obama and Hillary Clinton wings of the party. That could be a big problem heading forward. The RNC, in the meantime, is more closely affiliated with President Trump, who remains popular with the GOP base and helps the national party raise cash. Super-PAC spending also tends to favor Republicans.

Cole said that some members needed to wake up and realize they face tough reelection fights and that he expected GOP leaders to try to push them to get moving.

“I don’t have sympathy with people who don’t go raise money,” he said. “I expect there’ll be a lot of kicks in the rear going forward.”

This story was updated to correctly identify Rep. Steve Knight’s (R-CA) home state.