We are living in interesting times. Some might even say “desperate.” I’m speaking mainly about the presidency of Donald Trump. In Maine, we must also contend with a governor named Paul LePage. Then there’s this.

On Jan. 21, 2017, the day after Mr. Trump was inaugurated as our 45th president, my 33-year-old son, Mark Baumer, was hit and killed while walking across America to raise awareness about climate change. For the past year, I have been passing through grief and loss, while also witnessing the unraveling of the nation I’ve lived in for 55 years.

Mark Baumer posted this photo of himself on his blog on Jan. 15, when he was in Florida. Baumer was walking across America to raise awareness about climate change when he was fatally struck by an SUV.

Mark’s final walk (one that he was doing barefoot) was an attempt to up the ante and raise awareness about climate change. He also had a goal of raising $10,000 to help support the work of a Providence, Rhode Island-based social justice collective, FANG, standing against the proliferation of petroleum-based pipelines. Mark, who grew up in Maine and graduated from Greely High School in Cumberland, had settled in Providence, where he worked and owned a home.

We are coming up on the anniversary of losing our only son. He would have turned 34 the week before Christmas. This is a difficult season of first anniversaries for us.

Because of that, I have grown especially sensitive to attempts by politicians to “profit as the world burns,” something Mark said about President Trump on his final video, posted to YouTube the day before he was killed in the Florida Panhandle, after being struck by an SUV while walking against traffic in the middle of the paved breakdown lane on U.S. 90.

Imagine my own feelings last Sunday, when I read in this newspaper that our governor is the outlier among 16 governors of coastal states as the sole supporter of the Trump administration’s lifting of the ban on offshore oil and gas exploration. His stance greatly increases the possibility of drilling in coastal areas, which would surely have a negative effect on Maine’s vulnerable fishing and lobstering industries.

Mark posted 100 daily videos and blog posts from the road. He shot and edited these on his phone. He wrote poems while he walked. Thousands were following him, watching this poet, performance artist and activist walking barefoot, while capturing the country most of us have seen only from the window of a plane. He was an outspoken crusader for protecting our planet. He believed that humans don’t have the right to despoil the natural beauty of Earth and that doing so would be to our own peril as a species.

The day Mr. Trump took his oath of office, I spoke with Mark by phone. I’d called him after feeling deflated, after watching the swearing-in ceremony of the new president. It was hard to imagine anyone acting more boorish or arrogant. Of course, we know that this was just a preview of what was ahead. Mainers know all too well what arrogance in leadership looks like, given the past seven years of Mr. LePage leading with a similarly imperious style.

Our final father-and-son conversation touched on that. We also got to say the things that all fathers and sons should always make sure to say to one another. He knew I loved him, and he reciprocated by telling me that he loved me and was proud of me as a dad. Less than 24 hours later, he was dead.

Mark unleashed an uncharacteristic jeremiad in his final video. It was prophetic about our current president. I think he also clearly delineated politicians like Paul LePage, who regularly ignores science, while hearkening back to a bygone “golden age” of nonrenewable energy policy, reliant primarily on oil and natural gas.

Dealing with leaders like Donald Trump and Paul LePage, who see Earth as merely something to exploit and profit from, it’s all too easy to become desensitized and resort to social media-based hand-wringing. But Mark’s example also offers us a model for “resistance” and, I believe, a viable way forward. My son tended to downplay any suggestion that he was doing something heroic. During a video he posted from Day 92, he offered up this to viewers as a way to live: “Protect the Earth and treat everyone with love and kindness.” That’s a good start.

I’d also offer up that small acts add up to something much greater. Since Mark was an activist, moving past mourning and organizing is the way forward to all of us who want something better for America than the hate, racism and xenophobia dressed as populism that Trump offers us, and short-sighted energy policies for Maine from our current governor.

I know that’s what Mark would have expected from us.

Jim Baumer of Brunswick is a writer and president of the Mark Baumer Sustainability Fund (markbaumersustainabilityfund.org), a nonprofit foundation focused on creating a world built on love, kindness and ensuring a better and more equitable environment for all people.