Theodore Roosevelt, who saved over 234 million acres of wild America as president from 1901 to 1909, was so taken with “The Maine Woods” and “Walking” that as a Harvard undergraduate he climbed Mount Katahdin to follow in Thoreau’s footsteps. Around 2000, a modern-day Thoreauvian, Roxanne Quimby, co-founder of Burt’s Bees, started buying up the Maine acreage her literary hero often tramped. Once Quimby acquired Thoreau’s North Woods stamping grounds she donated 87,563 acres to the Interior Department. In August 2016, President Obama, on the eve of the National Park Service centennial, established Katahdin Woods and Waters National Monument from her holdings. (Sadly, the Trump administration is now reviewing opening it to timber harvesting and hunting. )

Rose Kennedy, the mother of the 35th president, spent much of her childhood in Concord, and she treasured both the book “Walden” and the pond. When her husband, Joseph Kennedy, bought a home in Hyannis Port in 1928, she read Thoreau’s less well-known “Cape Cod” (1865) and was awe-struck. Thoreau had first hiked the Outer Cape’s shoreline in 1849 and began composing reflections for public lectures. Young Jack Kennedy, influenced by his mother, adopted Thoreau’s elevated notion of Cape Cod as being where “a man can stand” and “put all of America behind him” as his own.

Coinciding with the Kennedys’ move to Cape Cod was the publication of Henry Beston’s book “The Outermost House” (1928). Beston spent a solitary year on the Outer Cape, journaling about the migrations of shore and seabirds, the headlong waves, the glories of sand dunes, the pageantry of the stars. Born in 1888 to an upper-middle-class Catholic clan in Quincy, Mass., Beston was encouraged at an early age by his parents to explore the Cape. As an Atlantic Monthly correspondent, a farmer of herbs, a rustic wanderer and a writer of children’s books, Beston fell in love with the primitive grandeur of the New England seaside. When he turned 38, he purchased 50 acres of dunes near the town of Eastham on the outermost beach of Cape Cod. His small Fo’castle residence — a locally built home with 10 windows offering unobstructed views of the Atlantic — offered Beston the kind of Walden-like solitude he craved. The National Park Service of the 1950s adopted “The Outermost House” and “Cape Cod” as justifications for establishing a 44,000-acre national seashore of secluded beaches and mysterious bogs in coastal Massachusetts. Likewise, Senator John Kennedy, inspired by Thoreau and Beston, introduced legislation in 1959 to establish Cape Cod National Seashore.

Just as Muir’s book “Our National Parks” had helped save the High Sierras of California, “Cape Cod” served as an important catalyst for protecting what Thoreau called “the bared and bended arm of Massachusetts.” In a 1959 New York Times article titled “Walking in Thoreau’s Footsteps on Cape Cod,” Caroline Bates enthusiastically embraced the national seashore effort. “The adventurer in search of wild America,” she wrote, “visits this coast for the same reason that Thoreau did.” As president, in 1961, Kennedy pushed a Cape Cod N.S. bill through Congress. (The Trump administration, in an unprecedented act, has suspended the local commission that regulates Cape Cod N.S. in possible preparation for gutting environmental protections there.)

Thoreau became the all-seasons environmental guru of the Long Sixties (1960–74). After Rachel Carson learned she had breast cancer, she adopted a sentence from “Walden,” which she always kept at her bedside, to spur on her writing of “Silent Spring”: “If thou art a writer, write as if thy time were short, for it is indeed short at the longest.” Howard Zahniser of the Wilderness Society used the “in wildness” quote on his nonprofit’s stationery. David Brower of the Sierra Club published a book titled “In Wildness Is the Preservation of the World” with excerpts from Thoreau’s nature writings accompanied by the landscape photography of Eliot Porter. “To me, it seems that much of what Henry David Thoreau wrote more than a century ago was less timely in his day than it is on ours,” Brower offered in the introduction.