On Thursday, President Obama touched down here, a sliver of land in the North Pacific so removed from other human development that it feels like the edge of the universe. For more than two years, he had been hoping to visit a place like this, even though his then-senior counselor John D. Podesta told him America’s most pristine marine reserves are “the middle of nowhere.”

But here, surrounded by the ocean and a population of seabirds so vast that it dictates when planes can fly certain times of the year, Obama celebrated his most dramatic action yet to safeguard the planet against climate change.

The president used the Midway visit to tout his decision last week to expand the Papahanaumokuakea Marine National Monument to more than half a million square miles, making it the largest ecological preserve on Earth. After touching down, he gawked at a handful of threatened green sea turtles basking in the sun as small white terns glided nearby. He zipped along in a golf-cart motorcade on an island 1,300 miles north of Hono­lulu that used to serve as a critical U.S. military outpost.

Teeming with life — from the more than 1 million albatrosses that flock there every year to the endangered Hawaiian monk seals that haul themselves on land to pup — the monument area contains some of the world’s most undisturbed habitats. Obama said that preserving it would allow us to “research and understand our oceans better than we ever have before,” in an era where they are under pressure from climate change.

“This is going to be a precious resource for generations to come,” he declared, standing on a pier.

“This is an area twice the size of Texas that’s going to be protected, and it allows us to save and study the fragile ecosystem threatened by climate change,” he earlier told a group of Pacific Islands leaders and conservationists gathered at the University of Hawaii’s East-West Center.

“These animals, and these creatures, are surviving at the edge,” said Aulani Wilhelm, who served as the monument’s superintendent for eight years and is now vice president of Conservation International’s Oceans Center. “You see these animals in huge, massive volumes. Then you realize how they’re really on the brink, when you see the small patches of lands they’re dependent on for survival.”

With less than half a year left in office, Obama may have fully entered the grand-gesture phase of his presidency — the time when outgoing presidents seek to broker last-minute peace deals, finalize regulations and deliver sweeping valedictory addresses.

Sen. Brian Schatz (D-Hawaii) said it helped that Hawaii is the president’s home state.

“The sense here is that there’s an emotional connection to the islands and to the ocean in particular,” Schatz said

As they search for opportunities to do something both big and feasible, commanders in chief often turn to the Antiquities Act of 1906. Theodore Roosevelt designated the Grand Canyon a national monument shortly before leaving office. Bill Clinton used his last appearance in the East Room on Jan. 17, 2001, to designate two monuments in Montana along the trail William Clark and Meriwether Lewis explored two centuries before and to posthumously promote Clark to captain. He also elevated Sacagawea, the legendary Shoshone woman who was crucial to the Lewis and Clark expedition, and the explorers’ slave, York, to sergeants in the U.S. Army.

James L. Connaughton, who led the White House Council on Environmental Quality under George W. Bush and played a key role in persuading his boss to designate the area in the northern Hawaiian islands as a national monument a decade ago, said it is the expanse of the environment that makes it special.

“It’s the scale,” Connaughton said. “It’s the drama; it’s the biodiversity that just carries an overwhelming appeal.”

Bush called Connaughton back from his Thanksgiving vacation in 2008 to pore over three maps — each of which took up the entire table in the dining room off the Oval Office — to strategize how to create what became the Pacific Remote Islands Marine National Monument just weeks before he left the White House.

During his first term, Obama declared four monuments spanning less than 20,000 acres. In his second, he has established or enlarged 22, encompassing almost 550 million acres. The second-term pace has had environmentalists cheering, but it ruffled feathers among Republicans who see the president’s actions as an unconstitutional overreach.

House Natural Resources Committee Chairman Rob Bishop (R-Utah) believes that the president’s willingness to invoke his executive authority so frequently only after his reelection “makes it unique, or at least questionable.”

“They’re violating the letter of the law, and it doesn’t seem like a legitimate effort if they’re not willing to do it if they’re going to have to face the voters afterwards,” Bishop said.

Six other presidents have provided federal safeguards for the Northwestern Hawaiian Islands. But back then the threats — poaching and overfishing — seemed more straightforward.

Roosevelt dispatched the Navy there when he learned albatrosses were being slaughtered so their feathers could decorate ladies’ hats, and he declared the Hawaiian Islands Bird Reservation in 1909. Franklin D. Roosevelt, Lyndon B. Johnson, Ronald Reagan, Clinton and Bush broadened protections for the area.

A few presidents have been ready to go quietly, forgoing late-stage theatrics either because they were demoralized or had little appetite left for a fight. But most push until the very end, especially those who still, in the words of presidential scholar Stephen Hess, “have too much juice flowing through their veins.”

Clinton was not only declaring monuments at the end. He brought Israeli Prime Minister Ehud Barack and Palestinian leader Yasser Arafat to Camp David in the summer of 2000 to try to end the Israeli-Palestinian conflict. Shortly before stepping down, Clinton finalized a slew of regulations, including one barring road construction in 58.5 million acres of national forests.

Obama’s ambitions are just as broad. His aides are finalizing rules that would require federal contractors to provide paid sick leave and tighten energy efficiency standards for items including residential furnaces and lightbulbs. And he is eyeing additional national monuments that could include deep-sea canyons off the New England coast and an ancient Native American site in southeastern Utah.

When Obama expanded the Pacific Remote Islands Marine National Monument in 2014, he told Podesta, then a White House senior adviser, that he wanted to see the protected islands, atolls and reefs for himself.

“He wanted to go there,” Podesta said in an interview on Tuesday, “and now, lo and behold.”