By Adam Kaye

When Parker Cornell runs along the rugged terrain at Mission Trails Regional Park, his thoughts often turn to his 9-year-old buddy with a brain tumor. The boy is fighting for his life. Cornell visits him and his little brother and does what he can to boost their spirits. In April, he will run the Boston Marathon to raise money for the young cancer patient and his family.

Cornell, a Navy SEAL and volunteer with One Summit, a SEAL-founded charity for pediatric cancer patients, sees himself as a motivator.

But that motivation works both ways.

Cornell is transitioning out of the SEALs after a head injury and subsequent diagnoses of multiple sclerosis and Lyme disease. But he refuses to feel sorry for himself.

“I can’t feel too badly for myself when I look at a 9-year-old whose outlook is bleak and his 6-year-old little brother who’s losing his idol,” Cornell said.

Cornell, 26 and married and now residing in Mission Valley, has come a long way since his mischievous-but-honor-student days at Carlsbad High School, where he wrestled and swam competitively.

While swimming those laps, he pictured himself swimming bombs up to enemy ships. In fact, joining the SEALs had been a “missile-lock” goal of Cornell’s since the fourth grade, he said.

In 2014, Cornell enlisted in the Navy as a sailor and soon shipped out to Naval Station Great Lakes for basic training. During his time at the sprawling installation in Michigan, Cornell met the standards and physical requirements to secure a special warfare operator contact and ticket back to San Diego to begin basic underwater demolition training at Naval Base Coronado.

In November 2016, became a Navy SEAL. He was assigned to SEAL Team 5.

And the training, of course, continued.

During one exercise, at around sunset on a November afternoon in 2017, Cornell was laden with gear as he climbed into a helicopter. The Sikorsky Seahawk was hovering at about 20 feet. Cornell somehow became caught on the wire ladder. A buddy reached for his hand. Cornell’s hand slipped. Down he went.

He landed on his head.

A teammate fast-roped down from the airship and found Cornell was unconscious. The injured SEAL was rushed to a hospital.

The initial diagnosis was traumatic brain injury and his symptoms — tinnitus, forgetfulness, fatigue, trouble concentrating — seemed to back it up.

Doctor visits continued. Brain scans revealed lesions and a spinal tap later confirmed a diagnosis of multiple sclerosis. Months later, further analysis uncovered a second neurological condition: Lyme disease.

“I had no idea,” Cornell said.

Today, Cornell remains on active duty as he awaits a formal determination from a medical review board. That should happen in March. In all likelihood, he will be forced to retire from the SEALs.

Meanwhile, there’s that marathon to train for and next steps to consider. He also has accomplishments to reflect proudly upon during the past year.

Cornell recently completed the transition program at The Honor Foundation, an institute that provides professional development for Navy SEALs as they prepare to enter civilian life.

He attended thanks to support from a grant-making organization that saw his great potential as a champion for pediatric cancer patients.

The Harbaugh Foundation — which supports military causes, pediatric cancer research, open space preservation and other pursuits — works closely with The Honor Foundation.

“Supporting Parker with a scholarship, that was a no-brainer,” said Joe Balla, director of The Harbaugh Foundation. “We were proud to name Parker Cornell as the Harbaugh Fellow for 2019.”

In that role, Cornell represented The Harbaugh Foundation in January as an official ambassador at the Patriots’ Outpost, a VIP pavilion for military personnel at the Farmers Insurance Open golf tournament. He appeared in television interviews and promoted the Patriots’ Outpost as a special place where freedom fighters get a front-row seat and the appreciation they deserve.

During the tournament, Cornell greeted dignitaries and smiled for the camera with a fresh face and easy charm that gave no hint of his having been trained to fight at the highest level for the United States government.

Today, Cornell’s training involves lacing up those running shoes and logging some miles.

“As many as I can whenever I can,” he said.

That and lifting weights.

One of the driving forces behind his regimen is Keith Eckert, a runner of 200-mile races, fitness instructor and skydiver who had his own experience with a medical discharge from the military.

“Keith motivated me to redefine the disease,” Cornell said. “Nothing’s impossible. You can keep pushing. Always.”

Cornell has pushed himself during eight previous fundraising events for One Summit. Based in a Boston, One Summit is on a mission to build resilience in pediatric cancer patients by pairing them with Navy SEALs like Cornell, who mentor and motivate the kids to complete the “Climb for Courage” on an indoor rock-climbing wall. That challenge, and the bonds they build with their SEAL buddies, goes a long way toward helping the children conquer the adversity they face.

When Cornell runs the Boston Marathon, the kids he mentors will be right on the sidelines.

“I’ll show these kids that nothing can keep you down,” he said.

Where is all of this leading a Navy SEAL who is facing big changes of his own?

“I’m keeping my ears and eyes open,” Cornell said. “I want to be in a selfless role that positively impacts the lives of others in any way I can.”

Visit Cornell’s fundraising page at crowdrise.com/parkercornell.

—Adam Kaye writes on behalf of The Harbaugh Foundation.