The day after Trump's win, the ACLU published an open letter to him on their site, then took out a full-page ad in the New York Times:

If you do not reverse course and instead endeavor to make these campaign promises a reality, you will have to contend with the full firepower of the ACLU at every step. Our staff of litigators and activists in every state, thousands of volunteers and millions of card-carrying members and supporters are ready to fight against any encroachment on our cherished freedoms and rights.

Right now their website is very focused on fighting Trump and his policies. He's been huge for fundraising:

This is the greatest outpouring of support for the ACLU in our nearly 100-year history, greater than the days after 9/11.

ACLU will be getting a big donation from me this year. You should donate too. And check if your company matches donations to increase your impact.