But just since Election Day, he said, the A.C.L.U. has surged to more than a million members and — as of 5 p.m. Monday — it had taken in $71.3 million from 921,304 online donations; $31.5 million of that came from 456,714 since Friday, when Mr. Trump signed the travel ban. The money will fund many more lawyers at both the federal and state level, he said.

“It’s extraordinary — we’ve never seen anything like this,” Mr. Romero said. “It means that people expect us to do a lot more of this work.”

Other organizations also reported a surge in fund-raising and interest. Caroline Fredrickson, the executive director of the American Constitution Society, said that when her organization sponsors a conference call to discuss an issue, it typically gets 80 to 100 R.S.V.P.s. On Monday, it announced a call about the travel ban and got 500, she said.

Similarly, Nan Aron, the president of the liberal Alliance for Justice, which focuses on judicial nominations, said in the past her group has had trouble getting support from corporate law firms that seek to avoid entanglement in politics, but since the election, several “major” ones — she would not name them — have volunteered their services to research the backgrounds and records of potential judicial nominees.

“The bar has been galvanized in a way I have not seen since the 1960s,” she said. “They are just showering us with offers of legal assistance.”

New liberal legal groups are also sprouting up. The day after the election, Traci Feit Love, an Atlanta-based lawyer, created a private Facebook group she called Lawyers for Good Government, hoping, she said, to get about 200 members who wanted to discuss the changes that were coming.