— The announcement last week that former U.S. Sen. Mary Landrieu has signed on to work for a D.C. lobbying firm generated a feeling of smug satisfaction in at least some element of the Louisiana electorate, of the “I told you so” variety.

The news seemed to confirm the accusations made against her by her Republican opponent, Bill Cassidy, in his successful campaign last year to replace her in the Senate. In a dispute over Landrieu’s residency, Cassidy said, “She literally no longer lives here. She belongs in Washington, D.C.”

That controversy flared up after Republicans questioned Landrieu’s qualifications to run for office. Landrieu, a Democrat first elected to the Senate in 1996, had effectively moved to D.C. soon after, and she raised her family in the house she and her husband built near the U.S. Capitol.

Legal challenges to Landrieu’s residency fizzled out, although Republicans made hay with the issue in the campaign. Now, it appears, there was something to what they said.

Or not.

It turns out that Landrieu’s move is par for the course among former member of Congress — senators and representatives, Democrats and Republicans — regardless of whether they ever faced accusations that they no longer resided in their home states. Hundreds of ex-members work for D.C. lobbying firms or perform similar work as the titular heads of trade associations and other interest groups.

Louisiana is well represented in those ranks. Current or recent D.C. professional persuaders who once served the state in Congress include former Sens. John Breaux and J. Bennett Johnston Jr. and former Rep. Charles Melancon, all Democrats, and former Republican congressmen Rodney Alexander, Richard Baker, Bob Livingston, Jim McCrery, Henson Moore and Billy Tauzin, according to the nonpartisan Center for Responsive Politics. McCrery actually did run into a residency controversy of his own when he sold his home in Shreveport in 2004 and moved his family to Northern Virginia, but that neither cost him his job nor re-election in 2006.

An ex-member of Congress, Livingston said, brings unique skills to the job.

“You’ve been through the process; you know the process,” he said. “Your average business, large or small, has very few people who know anything about the legislative process. They need advice.”

Johnston’s son, Hunter, who is also a Washington lobbyist, said, “It’s no secret that there is a robust employment market for people with knowledge of the government in the Washington consulting world.”

Landrieu is barred by federal law and Senate rules from directly lobbying members of Congress until January 2017 — two years after the end of her term. Direct lobbying includes talking to, calling, emailing or otherwise communicating with a member about an issue before Congress.

But she can offer pointers on strategy to her new firm, Van Ness Feldman. “She can visit with clients and give them advice and let them know if they have a shot,” Livingston said.

Once the ban expires, Landrieu’s experience in the Senate should help her cash in with the coin of the realm in the lobbying arena: access.

“She’s got personal relationships with a lot of members of Congress,” Hunter Johnston said.

She may have to go some to match Tauzin: He earned $11.6 million as head of a drug-industry group in 2010, the year he helped negotiate an agreement on the Affordable Care Act health law. Tauzin now runs his own firm in D.C.

In a news release on her hiring by Van Ness Feldman, Landrieu said, “I have always respected the firm and worked closely with them during my 18 years in the Senate.”

Van Ness Feldman represents several clients in the energy industry, including the company that wants to build the Keystone XL pipeline from Canada to the Texas Gulf Coast and the backers of the Cameron Sempra liquid natural gas export facility in Louisiana — both projects Landrieu championed in Congress. Landrieu spent her last year in office as the chairwoman of the Energy and Natural Resources Committee, the top energy policymaking position in the Senate.

Landrieu’s relationship with Van Ness Feldman went beyond their shared interest in issues. Although other lobbying firms donated more to Landrieu, Van Ness Feldman gave more campaign money to her in the 2014 election cycle than it did to any other member of Congress, according to the Center for Responsive Politics: $21,850, accounting for nearly one-fifth of the total contributed to members of Congress by the firm’s employees and its political action committee.

Gregory Roberts is chief of The Advocate Washington bureau. His email address is groberts@theadvocate.com, and he is on Twitter, @GregRobertsDC. For more coverage of national government and politics, follow The Advocate Politics Blog at http://blogs.the advocate.com/politicsblog.