David Robinson upended his life after terrorists attacked America on Sept. 11, 2001, selling his trucking business to join the Army, where he served two tours in Afghanistan before suffering injuries in an IED blast.

"I joined the military when duty called to fight for our country, defend our democracy, defend our way of life," he told Fox News Digital. 

Decades later, his life changed again when his geologist son vanished without a trace from a well site in Arizona. Now he's running for Congress with a focus on missing persons across the country.

He served as a combat engineer until he retired from the Army and moved on to open a new business in his hometown of Columbia, South Carolina, he said. But his son's disappearance sent him to another desert, this one on the other side of the country, in search of answers.

ARMY VET SAYS NEW EVIDENCE SUGGESTS FOUL PLAY IN UNSOLVED DISAPPEARANCE OF SCIENTIST SON

David Robinson with his father

Missing geologist Daniel Robinson, left, and his father, David Robinson II, are shown in this undated photo provided by the family. (David Robinson II)

"I'm sitting right here in this very seat, and I see that phone call from Arizona. My daughter called me, and I ended up in the Sonoran Desert of Arizona," he told Fox News Digital. 

"My journey from there came to a point of running [for Congress], when you get sick and tired," he said. 

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He wasn't making progress in the search for his son, he said, but he was meeting more and more families of missing Americans

David Robinson sitting on rock

Daniel Robinson is shown in this undated photo provided by his father. (David Robinson II)

"I had families out there with missing loved ones of their own," he said. "You learn a lot. … I went to meetings with the telecommunications [companies], talking to the senators, to you name it, law enforcement agencies. And I learned the ins and outs of things that are not being correct, the policies and the laws that are in place that actually hurt efforts to find missing Americans."

One problem with the way cases are investigated is how phone records are approached, he said. Telecommunications companies usually ask to see a warrant before providing information such as cellphone pings, he said.

MISSING ARIZONA GEOLOGIST DANIEL ROBINSON: A FATHER'S UNENDING SEARCH FOR HIS SON, 1 YEAR LATER

David Robinson and Candice Cooley pose in a hallway at a conference center

David Robinson, right, is shown with Candice Cooley, whose son, Dylan Rounds, vanished from his own Utah farm and was later found to have been killed by a squatter next door. They are part of a community of parents of young Americans who went missing. (Michael Ruiz/Fox News Digital)

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"Sometimes when that happens, it's too late," he said. "The other problem is law enforcement cannot do it unless it's a criminal case, or they fear that a person is in severe danger, or something's out of order." 

In cases like his son's, although the circumstances remain a mystery, there wasn't a probable cause right away, he said. His wrecked Jeep wasn't discovered until almost a month after he went missing. But his son's phone account was under his daughter's name, and she paid the bill.

"That's problematic for a family," he said. 

MISSING ARIZONA GEOLOGIST: NEW DETAILS RELEASED IN DISAPPEARANCE OF DANIEL ROBINSON

He would propose legislation that makes data on an account available to the person paying the bill immediately, he said. Or at least to law enforcement upon the account owner's request – with exceptions built in for domestic violence cases.

David Robinson on stage along with the parents of Gabby Petito and Candice Cooley, the mother of Dylan Rounds

David Robinson, center, takes part in a panel discussion with the parents of Gabby Petito and Dylan Rounds, two other young Americans who went missing under suspicious circumstances. (Michael Ruiz/Fox News Digital)

Data retention is another issue. If police don't get a warrant in time, crucial information might be lost, he said.

There are other, traditional issues in his campaign platform as well, ranging from education in his district to the cost of prescription drugs, abortion and climate change.

Daniel Robinson, a geologist working for an energy company in Arizona, vanished from a remote job site in June 2021.

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Daniel Robinson's jeep and Daniel Robinson

These images show Daniel Robinson's crashed 2017 Jeep Renegade and Daniel Robinson in an undated photo. (Buckeye Police Department)

Buckeye police last year published more than 120 pages of investigators' records in the case, which remains unsolved.

"There was no indication of foul play," a detective wrote in a supplemental report, but there was also "no indication that Daniel had packed and planned a trip."

On July 19, 2021, a rancher located Robinson’s 2017 Jeep Renegade battered and rolled onto its passenger side in a ravine. The vehicle had front-end impact damage, a broken driver's side window and a missing piece of its roof. It was still in drive. There was no blood inside.

Police found clothes, Robinson's phone and work computer inside. His wallet had no cash inside. But there was no sign of the missing geologist.

Daniel Robinson with hard hat on

Daniel Robinson is shown in this undated photo provided by his father. (David Robinson II)

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Robinson faces an uphill battle, however. He is running as a Democrat in a district that has consistently elected a Republican to Congress since 1965.

The seat is currently held by Rep. Joe Wilson, a fellow Army veteran who first won the office in 2001.

Both men are running in their respective parties' primary elections, scheduled for June 11.