In a self-important, gossipy town like Washington, D.C., where almost no conversation is safe from leaks, there is one bastion of secrecy on Capitol Hill.
The Chowder and Marching Club is kept so far under wraps that members are reluctant to even acknowledge its existence. “I don’t even know what you are talking about,” said U.S. Rep. Ileana Ros-Lehtinen of Florida.
When reminded she had tweeted a photo of herself in 2014 wearing a chef’s toque and striped apron emblazoned with “Chowder and Marching”—the garb worn at club banquets—Ms. Ros-Lehtinen acknowledged her slip.
“They probably choked me after that,” she said. “The first rule about Chowder is that we don’t talk about Chowder.”
All the secrecy seems anachronistic at a time when hardly a meal is eaten in America without a photo posted on Instagram.
These tidbits are known: The Chowder and Marching Club is an invitation-only group of current and former House Republicans that has been around almost 70 years. They meet Wednesday evenings in the U.S. Capitol. Once every few years, members gather for a banquet wearing aprons and goofy hats that resemble the Swedish chef character from “The Muppet Show.”
Confidential interviews with skittish club members have uncovered more. The club meetings, held every week the House is in session, encompass an hour of drinks, dinner and conversation about policy and politics. They are held on the Capitol’s first floor, in Room H-107.
Even the club’s name is a mystery. Members say they aren’t sure of its origin. Groups bearing the name Chowder and Marching date back to the 1800s, spanning sports teams to community service groups.
Washington’s secret club was co-founded in 1949 by then-House members Richard Nixon and Gerald Ford. According to the House historian’s office, the group grew out of the opposition from younger lawmakers to a veterans pension bill that had been rammed through the Veterans’ Affairs Committee by its powerful chairman. Questioning the bill’s need and cost, the junior members assembled to sink the bill. They succeeded.
From that grew a club with no specific agenda, unlike most other groups on Capitol Hill. “It’s not like legislation comes out of it,” said one member who confirmed his membership on the condition he not be named.
The club’s aim is simply to provide a venue for legislators, young and old, to meet, network and shoot the breeze. Its membership of a few dozen is built every year by invitation. Members tap a handful of recently elected House members who seem to have promising careers ahead of them in Congress, regardless of ideology.
Women have been included since the early 1990s, when U.S. Rep. Tillie Fowler of Florida and Ms. Ros-Lehtinen became the first female members, according to the book “Congressional Women: Their Recruitment, Integration and Behavior” by political scientist Irwin Gertzog.
Beside secrecy, another club rule is once a Chowder member, always a Chowder member. Lawmakers who leave the House for the Senate or governorships—or even the private sector—are forever welcome at meetings.
That explains why former Senate Majority Leader Trent Lott of Mississippi, now a lobbyist, is often spotted in the halls of the Capitol late Wednesdays.
Meetings take place in a conference room in the suite of House Majority Leader Kevin McCarthy of California. Sitting House members have priority to address the meeting, one of the few places in Washington where senators defer to the lower chamber.
Members take turns providing the chow, which leans casual—sometimes from a local fast-food joint, paper napkins included. Sometimes, meals are shipped from a member’s district.
Its select membership is heavy on Republican traditionalists and power brokers, including the House committee chairs and members of the Senate GOP leadership. Its 1970s rolls included luminaries like Jack Kemp, Melvin Laird and Robert Michel as well as Messrs. Nixon and Ford.
The club is a refuge for old-guard Republicans in President Donald Trump’s Washington, one old-time member said, a meeting place for politicians with a now-unfashionable love of politics and governing.
“These are the people who are institutionalists, not disrupters,” the member said. “If the president walked in and looked at this group he’d say, ‘This is the Swamp.’ They’d look at him and say, ‘This is amateur night at the Bijou.’”
Meetings provide these Republicans a weekly escape from the political storms that sweep daily across D.C. It is so cloistered that the day House Speaker Paul Ryan announced he was going to retire, Chowder members met and chatted casually about other matters. Finally, a former House member asked about the “elephant in the room,” and the gossip commenced.
As the group met one recent Wednesday, other lawmakers ambled by the closed-door meeting, unaware of the huddle inside.
“I have no idea,” said U.S. Rep. Mo Brooks, an Alabama Republican. “I know what chowder is, I like it. Marching is OK until you do too much of it.”
Just asking about the club makes its members squirm and sputter denials or no-comments. One Republican lawmaker switched to the subjunctive.
“If I were in Chowder and Marching, I would think it would be a place some folks could go and talk about what’s going on politically in their state and district,” said the lawmaker, whose membership was leaked by a colleague.
Then he surrendered. “We can have a candid conversation at a very high level about not just the issues you are working on, but also sort of the underlying political environment that we’re operating in,” he said.
Ms. Ros-Lehtinen, a centrist Republican who is sometimes at odds with her increasingly conservative party, is retiring from Congress after this year. Still, she was reluctant to dish about the club.
“You know, I’m already so unpopular with the GOP leadership, with the Trump White House, I don’t think I can get another arrow in my back,” she said, reaching for an elevator button to get away from a reporter.
She paused a moment to reflect on how the party has changed since she was inducted more than 20 years ago. “Once upon a time, I was looked upon with good light,” she said, “but now I don’t think I could have made it.”
Then, as the elevator doors closed, she delivered a non-denial denial: “I love that imaginary organization.”
Write to Janet Hook at janet.hook@wsj.com and Natalie Andrews at Natalie.Andrews@wsj.com