Out of the presidents I will mention below, which spent a summer at Yellowstone National Park as a Ranger?

Chester A. Arthur was the first president to visit in 1883, President Theodore Roosevelt was the 2nd to visit in 1903. In 1923 - Warren G. Harding visited the park, in 1927 - Calvin Coolidge. In 1937 Franklin Delano Roosevelt spent some time away from a campaign tour to visit the park. FDR backed many measures to enlarge our national parks and to preserve wildlife.

Gerald Ford was President when he paid a visit in 1976. Jimmy Carter was focused on fishing during his visit. George H. W. Bush 1989, Bill Clinton has been there twice. President Barack Obama broke the rules when he got up close to a bison that could have been quite a challenge for his Secret Service detail had the animal gone rogue.

It was Gerald Ford who was a Park Ranger at Yellowstone National Park. In 1936, following his graduation from the University of Michigan and forty years before returning to the Park to speak as president, Ford worked for a summer as a park ranger, a job he cherished and one he discussed in his “Remarks at Yellowstone National Park In Wyoming”:

It “was one of the most challenging experiences, one of the greatest jobs I ever had.” – President Gerald Ford on his time as a ranger at Yellowstone.

“The 38th president of the US said working as a park ranger at Yellowstone National Park was "one of the greatest summers of my life," according to the Yellowstone Park Foundation.

The feeling is mutual: his supervisor at the park, Canyon District Ranger Frank Anderson, said Ford was "a darned good ranger."

"His most dangerous duty was working as an armed guard on the truck that fed the bears in the park. This high-risk job later became fodder for impressive stories to share with his kids.” - Inc

The Obama White House via YouTube