On Saturday, Steve Mendelsohn received an unexpected phone call.
A staff member with the HBO comedy show “Last Week Tonight With John Oliver” had a small question about the Trevor Project, the nonprofit where Mr. Mendelsohn works and which the show planned to feature in a comedic call to arms.
In the segment, which was broadcast the next day, Mr. Oliver urged viewers to donate to causes he felt were being threatened by President-elect Donald J. Trump — and to do so on behalf of friends or loved ones who voted for him. The list of groups he encouraged his audience to support included the Trevor Project, which provides help to lesbian, gay, bisexual and transgender youth.
“It’s working,” Mr. Mendelsohn, the nonprofit’s deputy executive director, said on Wednesday, adding that the on-air mention helped sustain an outpouring of donations that had begun in the days after the election.
The Trevor Project has company. At least a dozen nonprofits that oppose Mr. Trump’s policies or actions have reported similar, in some cases explosive, surges in support since Nov. 8.
The American Civil Liberties Union, which defends the rights of the individual, said on Monday that it had received more than $7 million from about 120,000 donations over the five days after the election. During the same period after the 2012 election, the group collected less than $28,000 from 354 donations.
“This is the greatest outpouring of support for the A.C.L.U. in our nearly 100-year history, greater than the days after 9/11,” Anthony D. Romero, the group’s executive director, said in a statement on Monday. “All of this support will be put to good use protecting the rights of all Americans.”
By the end of Tuesday, the group’s postelection tally had risen to nearly $9 million.
The Anti-Defamation League, which combats anti-Semitism and other forms of discrimination, saw a fiftyfold increase in online donations on the day after the election. The Council on American-Islamic Relations, a Muslim civil liberties and outreach group, gained more than 500 volunteers in the two days after the election. Naral Pro-Choice America, which fights for abortion access, reported on Wednesday that it had signed up 290 times as many volunteers since the election as in an average week.
The Disability Rights Education & Defense Fund, NAACP Legal Defense and Educational Fund, National Immigration Law Center and International Refugee Assistance Project have all reported an outpouring of support, too.