When you step into the room, you can tell this isn’t your typical night at the Heritage Foundation offices on Massachusetts Avenue Northeast. For starters, it’s the middle of the week, and wine and beer are flowing freely, while the pizza is served straight out of the box. This event is a little rough around the edges, but the attendees have reason to celebrate: Scott Brown won election to the United States Senate.

The crowd keeps trickling in and eventually climbs to about 100 people. Excitement carries over from the previous day’s election results, but plenty of people are also revved about tonight: Rep. Paul Ryan (R-Wis.) is slated to speak.

After a brief introduction, Ryan bounds to the lectern, beer in hand. The lawmaker quickly launches into an indictment on everything from federal spending to the tax code and the “entitlement state.—

After a 10-minute talk, Ryan moves into question-and-answer time, which allows the lawmaker to intermittently swig from his beer in between queries on the Roadmap for America’s Future Act, Ryan’s bill to address the budget; what the Republicans need to do to regain the majority; and Democrats’ plans on health care reform.

Welcome to the Prosperity Caucus, version 2010. Founded in 1986, the group has a simple purpose: to gather libertarian-minded economists, Hill staffers and academics over beer and pizza to hear someone talk about the burning policy issues of the day.

With Washington’s quick pace, group turnover has been the name of the game in the quarter-century that the Prosperity Caucus has been in business. But by tonight’s attendance, it’s pretty clear that a number of attendees are throwbacks themselves, guys — and the group is overwhelmingly male — who have been attending since they were new to Washington 25 years ago.

Ryan is a Prosperity Caucus original. He regularly attended while working for Sen. Bob Kasten (R-Wis.) in the early 1990s. After Kasten’s retirement, Ryan worked as legislative director to Sen. Sam Brownback (R-Kan.).

Ryan has long passed being a regular attendee or having the time to help run the group — it was his first return to the Prosperity Caucus in nearly a decade — but the group’s reins still rest on Capitol Hill. Ike Brannon, an economist with the Republican staff of the House Energy and Commerce Committee, is the man in charge today.

Brannon said he took on the role somewhat unintentionally. “It was kind of in a lull back in 2001 and 2002,— Brannon said. “A friend of mine and I were working at the Joint Economic Committee back then. … A couple people suggested that we take it over, so in 2003 we started it up again.—

Brannon devotes most of his time on behalf of the caucus to securing speakers.

The Prosperity Caucus was the brainchild of Ralph Benko, an attorney who fled New York for Washington during Ronald Reagan’s second term. After securing a civil servant job with the Department of Energy, Benko was ready to recruit for his cause: supply-side economics, the crux of which rested in low tax rates, hard money, free trade and gentle regulations.

“At the time, if you read the New York Times and the Washington Post, we were thick on the ground,— Benko said. “You couldn’t swing a dead cat in a room without hitting at least three supply-siders. … I looked around looking for all these supply-siders in whom at the end of the day I could make common cause, and I couldn’t find any. It was the weirdest thing.—

So Benko decided to do something about it. “I made it my mission to track down every arguable supply-sider in Washington,— he said. “If I read a quotation in the newspaper that sounded like it had supply-side connotations, I would just call them up.—

Benko easily drops the names of supply-side originalists, many of whom attended the Prosperity Caucus in its early days: Basil Petrou, Paul Craig Roberts, Arthur Laffer and Jude Wanniski.

Benko gathered a group for drinks at the Apple and Eve Bar in L’Enfant Plaza in 1986. The only agenda was to socialize. Upon leaving, everyone agreed that is was something that should be continued, so the task fell on Benko.

Eventually the group became too big for bars, so conservative think tanks or House committee rooms served as host, always with the accompaniment of beer and pizza and a $5 cover.

Back in the early days, Benko said there was an inside joke to the Prosperity Caucus. “Nobody ever made it explicit, but everybody got the joke — this was Jack Kemp’s team,— Benko said. “When Kemp got elected president, this was going to be the pool of talent from which he was going to be recruiting.—

Kemp, a New York Republican and an advocate of supply-side economics, did run for president in 1988, but he lost in the primary to George H.W. Bush. Kemp would go on to work in the Bush administration as secretary of Housing and Urban Development, taking many of the Prosperity Caucus faithful with him as staff.

In the early 1990s, the group peaked at nearly 900 members.

Benko led the group for six years before transferring leadership in 1992 to Stephen Moore, who was an economist at the Joint Economic Committee and is now a Wall Street Journal editorial board member. The group would have two other leadership successions before Brannon took over in 2003.

Brannon said he’s trying to usher the Prosperity Caucus into the age of social media. The group recently established a Web site and is revamping its Facebook page.

Ultimately, Brannon said he would be content if things didn’t change too much. Typically, monthly meetings number about 50 people, a quarter of whom are Hill staffers.

“My idea is to have a place where people who want to think about big thoughts, about long-term issues, can come and get together and argue about those things and meet other people like that,— Brannon said.

Regardless of what happens, the Prosperity Caucus’ staying power can’t be disputed. Ryan even immortalized the group with the name of his political action committee, the Prosperity PAC.

And Benko predicts that “things are going to be getting very, very interesting over the next couple of years, and this group, whether it’s on the surface or in its own quiet modest unassuming way, is going to be a key part of developing the solution to the incredible fiscal crisis that is about to come.—