If you’re concerned about Trump’s nominations, the most impactful thing you can do is to reach out to your US Senators and voice your opposition. A large volume of brief phone calls do make a difference at strategic times. Immediately after a nomination announcement is one of those strategic times, because they are figuring out how/whether to respond publicly. Democracy must be fought for even after elections have ended.
Contacting Senators from both parties also matters right now. The prevailing message in the media is that Dems need to cater even more to Republicans to win the next election, they need to hear your voice if you disagree with that.
The most effective phone calls take less than a minute: say your name, your city or ZIP code, and what you support/oppose, maybe a sentence on why. You’ll be marked down on a spread sheet that is discussed at the daily office strategy meeting.
Other actions like brief emails, meeting in-person at the district office, meeting in-person at the DC office, can also be effective, but take more time and energy. Emails aren’t always read right away like a phone call must be answered for example. And you generally need to make an appointment for an in-person meeting.
Being aware of local and state government is always a good thing to do and so much stuff is streamed since Covid. It makes you an informed voter and it’s where most of the stuff that impacts you will take place. Marijuana is one example of the impact of state law winning out despite federal law.
Reach out in any form you choose. Get to know them and what they stand for through their actions. Explain how things will effect you and people you know. Like anywhere else being an asshole is not the way to go. You might not change their mind but reminding them that everyday voters are paying attention has an effect even if you respectfully disagree.