Staff members on committees in Congress have also moved on. Perhaps the most high-profile departure this year was Mark Prater, the longtime tax counsel of the Senate Finance Committee who joined the tax advisory firm PricewaterhouseCoopers in June. In May, Brendan Dunn, the policy adviser and counsel to the Senate majority leader Mitch McConnell, left to become a policy partner at the lobbying firm Akin Gump to focus on tax policy matters.

The staff of the House Ways and Means Committee, which started the tax-writing process, has experienced an exodus of its own. David Stewart, the committee’s staff director, left this spring to take a job in the public policy practice of the law firm Squire Patton Boggs. The committee also lost its coalition director, its general counsel, a speechwriter and several communications aides to lobbying groups like the Chamber of Commerce or to jobs in government affairs at companies like Microsoft and MGM International.

Administration and congressional staff members can often double or triple their salaries while working a fraction of their government hours by joining lobbying firms.

The migration from lawmaking to lobbying has occurred under both Democratic and Republican presidents. Congressional staff members often make the switch after the enactment of major legislation, and experts who chart the influence of money in politics noted a similar trend, perhaps to a lesser degree, after the passage of the Affordable Care Act under President Barack Obama.

“This year, the revolving door is particularly swinging out of control,” said Craig Holman, government affairs lobbyist at Public Citizen, an advocacy group that promotes lobbying reform. “The midterm elections are coming up, which many expect to not go well for the Republicans, and this is the ideal opportunity for Republican congressional staff and administration officials to be able to cash in on what they have been doing the last year an a half.”

Upon taking office, Mr. Trump made moves to strengthen some of the lobbying restrictions put in place by Mr. Obama. But Mr. Trump weakened other rules, including one that allows departing executive branch officials to lobby the administration informally, as long as they are not registered lobbyists.

Paul Miller, president of the National Institute for Lobbying and Ethics, said that this has led to the growth of a shadow lobbying industry, where former government staff members take consulting and advisory jobs that are essentially lobbying under a different name.