The traffic jam of black SUVs in front of the Capitol Hill Club this week was a clear sign campaign fundraising has reached a fever pitch.

“The Capitol Hill Club looks like a mosh pit,” said Monica Notzon, a GOP fundraising consultant.

The private Republican club, which is steps from the Capitol, similar Democratic venues and popular Washington restaurants are booked up until Sept. 30 as candidates and members scramble to raise money before the third-quarter reporting deadline.

“We always see a big uptick [in fundraising] in September. Everybody wants to brag about how much they’ve raised come Sept. 30,” said Nancy Watzman, who directs the Sunlight Foundation’s fundraising monitoring project. “There are lots of examples of folks in tough races coming to town shaking the money tree.”

The Sunlight Foundation estimates there’s been at least 250 Washington fundraisers thus far in September.

Some of the events have featured appearances by leading Senate prospects from both parties, including Ohio Democrat Lee Fisher, Washington state Republican Dino Rossi and California Republican Carly Fiorina. Rossi and Fiorina were in town for fundraising events on Thursday.

And with many observers predicting sweeping GOP gains this cycle, Republican fundraisers say they’re encountering more and more open checkbooks.

“We’re seeing a huge increase in dollars, attendance and enthusiasm,” said Notzon. “There’s a real sense of enthusiasm, and the money is now following that enthusiasm.”

Many consultants consider the June Federal Election Commission report their focus in order to show a candidate is gaining support. But the third-quarter reports, which are due to the FEC by Oct. 15, reveal how much money a candidate has on hand in the crucial closing stages of a race.

“A candidate who’s going to make a serious play in their race is going to have to have a serious amount of money in cash on hand,” said Kenneth Christensen, a Democratic fundraising consultant.

Candidates must also file an Oct. 21 pre-election report, but observers say that report has little influence over how party resources get allocated. “In some ways, the later stuff, it’s not that important in terms of posturing,” said Watzman.

Christensen agreed that the later numbers aren’t crucial for formulating party strategy.

“The last 30 days, in terms of allocation of resources, is going to be based on internal polling — polling by the committees,” Christensen said. “As long as the campaign’s competitive, they’re going to allocate resources.”

There are some risks for candidates who make their way into Washington to raise money in the closing stages of a campaign.

A Democratic consultant drew attention to a Washington fundraiser Massachusetts Democrat Martha Coakley held in the closing stages of the special election race with now-Sen. Scott Brown (R-Mass.) by knocking a reporter down as she exited the event. It gave voters the impression Coakley was huddling with lobbyists instead of courting their votes.

Meanwhile, an Ohio Republican official pointed to Fisher’s Sept. 27 fundraiser that’s being headlined by Sen. Sherrod BrownSherrod Campbell BrownDem senators introduce bill to ban controversial voter purges The Hill's Morning Report — Sponsored by PhRMA — GOP lawmakers race to find an immigration fix Warren to put hold on Trump consumer bureau nominee MORE (D-Ohio) as one that may be problematic. According to an invitation, one of the co-hosts of the event is Herbert Hansell, who sits on the board of the National Committee on U.S.-China Relations, which promotes closer ties between the two countries.

The Ohio Republican official pointed out that Fisher has criticized Senate rival Rob PortmanRobert (Rob) Jones PortmanSenate moving ahead with border bill, despite Trump 13 GOP senators ask administration to pause separation of immigrant families Lawmakers, businesses await guidance on tax law MORE (R) for supporting “bad trade deals” that increased the U.S. trade deficit with China.

In response, the Fisher campaign noted that Portman was in Washington on Thursday for a fundraiser hosted by the lawfirm Davis and Harman.

“Congressman Portman has the unique distinction of being the number 1 GOP recipient of lobbyist money and the  number 2 recipient of Wall Street money ­­— and he earned that distinction by fighting for special interests during his 20 years in Washington, D.C.,” Holly Shulman, a spokeswoman for Fisher, said in a statement.

At times, the parties simply use a Washington fundraising trip as a reason for hitting a candidate.

Rossi was in Washington for Thursday fundraising events with Sen. Mike JohannsMichael (Mike) Owen JohannsMeet the Democratic sleeper candidate gunning for Senate in Nebraska Farmers, tax incentives can ease the pain of a smaller farm bill Lobbying World MORE (R-Neb.) and Sen. John BarrassoJohn Anthony BarrassoGOP senators introduce bill to prevent family separations at border Overnight Energy: Senate panel sets Pruitt hearing | Colorado joins California with tougher emissions rules | Court sides with Trump on coal leasing program Pruitt to testify before Senate panel in August MORE (R-Wyo.), which got the attention of the Democratic Senatorial Campaign Committee (DSCC).

“Though Dino Rossi is fundraising in Washington, D.C., today, back in Washington state he is suffering from the same incurable resistance he faced in his two failed gubernatorial runs,” the DSCC said in a memo titled “Dino Rossi’s Downward Spiral.”

Still, campaigns are reluctant to engage in on-the-record criticism against their rivals for fundraising in Washington, because the allegations can be turned around quickly. There are few candidates who refuse to accept money from political action committees or lobbyists.

And because the information isn’t publicly available, it’s difficult to track who’s dining with whom in Washington.

“It can very easily slip under the radar,” said Watzman.