The retirement of several powerful members of Congress is being felt across the lobbying industry, in which former staffers who used their ties to the lawmakers to help build businesses are being forced to rebrand themselves or risk becoming irrelevant.

The impact is likely to be greatest among tax lobbyists, a K Street specialty that is rich with former aides to Max Baucus (D-Mont.), who this month gave up his post as chairman of the Senate Finance Committee to become the U.S. ambassador to China.

But across a variety of areas, the departures from Congress — more than two dozen at last count — are prompting former Capitol Hill aides whose biographies boast of their high-level connections to try to reassure their clientele that they bring more to the job than links with their old bosses.

“What happens when your street cred is built upon your relationship with one particular member?” asked Chris Jones, a headhunter who helps place lobbyists. “Do you still have any street cred? That’s a big question.”

Beyond the Baucus network, the changes are likely to be felt most by lobbyists with ties to other outgoing chairmen, including Carl Levin (D-Mich.), who leads the Senate Armed Services Committee; John D. Rockefeller IV (D-W.Va.), who heads the Senate Commerce, Science and Transportation panel; Tom Harkin (D-Iowa), chair of the Health, Education, Labor and Pensions Committee; and Rep. Howard “Buck” McKeon (R-Calif.), chair of the House Armed Services Committee.

“You’ve got to be able to pivot in this town,” said Dawn Levy O’Donnell, who worked under Baucus at the Finance Committee and now runs her own tax lobbying firm. Her clients “didn’t hire me to get to Baucus,” she said. “They hired me because I know the issues and the process and how to navigate the committee.”

Such shifts are a part of the culture of K Street, where retirements from Congress — and defeats at the polls — can quickly reshape the power structure, increasing the value of some relationships and slashing that of others. Last month, for instance, Capitol Counsel, a leading tax lobbying firm, announced that it had hired Josh Kardon, who spent 17 years as chief of staff to Ron Wyden (D-Ore.), the new chairman of the Senate Finance Committee.

At the same time, many lobbyists whose Washington careers began on Capitol Hill have remained influential long after the members they worked for have left the scene. And, despite complaints about the outsize influence of those who pass through the “revolving door,” lobbyists say their relationships with individual members matter far less than in the past because of the rapid turnover in Congress, the end of earmarks and the legislative gridlock of recent years.

But in a tough lobbying marketplace, clients are paying close attention to the changes on Capitol Hill.

“If you’ve hired somebody who has sold themselves on their knowledge of or access to an individual, and they haven’t over the years built any other relationships, they’re likely to be sooner or later taken off the payroll,” said Will Ris, who runs the Washington office of American Airlines and has about a dozen outside lobbying firms on retainer. “That’s why they were there.”

Most former congressional aides are barred from lobbying for a year after they leave the Hill, and former insiders bristle at the suggestion that their ties to members can be converted into special treatment for their clients. Savvy lobbyists spend time getting to know new lawmakers and work to expand their practice to a broader set of members and a deeper policy expertise. And in this time of transition, they are talking a lot about that extended network of lawmakers and key staffers, and about their understanding of both process and priorities.

But Patrick Griffin, who served as legislative affairs director in the Clinton White House, said that when an influential lawmaker leaves the scene, there is still often a “branding blip. It’s like, ‘He died and, oops, did you die, too?’ ”

“These guys will have to be smart to rebrand and to make sure that it’s understood that their practice has not been just about that,” said Griffin, the academic director of American University’s Public Affairs and Advocacy Institute. “They’ll have to fight the assumptions, but I think it’s manageable on their end.”

The latest round of departures will be felt far beyond those with ties to outgoing chairmen. Several other lawmakers who have announced their retirement have long been leaders in their field. Chief among them is Rep. Henry A. Waxman (Calif.), the top Democrat on the House Energy and Commerce Committee and an influential figure on health policy.

“For Democrats who do health-care lobbying every day, it represents a big change for them,” said one top Republican lobbyist.

Alex Nock, a lobbyist who specializes in education, worked for Rep. George Miller (Calif.), the senior Democrat on the House Committee on Education and the Workforce, who is also retiring.

Nock said he has heard from clients who are worried about Miller’s departure and what it means for education policy. “People probably do think of me as a George Miller person, and I can’t change that,” Nock said. “But one of the things that I always did when I was on the committee, and have done since I left the committee, is to talk to all sorts of members, whether to talk about George Miller’s priorities or clients’ priorities.”

Jones, the headhunter, said lobbyists should be able to weather the storm. “If all of the sudden your old boss leaves, you’ve been working on those contacts with other people in Washington for so long you’re still going to have some relationships,” he said. “Your contacts aren’t going to completely dry up when the member leaves. They will decrease, certainly.”

What a departing lawmaker does next could also matter.

“If they leave town and retire peacefully, it won’t give former staffers as much cache,” Jones said. “But if they stay in the mix . . . that will help.”

O’Donnell, the former Finance Committee staffer, is optimistic about her post-Baucus business. “If you’re a substance person and you have institutional knowledge, then you know what’s what,” she said. “It shouldn’t matter who is in charge.”