In Koessel v. Sublette County Sheriff's Department, the key litigated issue was whether the plaintiff successfully established that he could perform the essential functions of his job with or without a reasonable accommodation where he:

Kevin Koessel was working as a patrol officer with the Sublette County Sheriff's Office when he suffered a stroke. He was placed on administrative leave while he recovered, and returned to work part-time in a temporary office job several months later. Koessel continued the desk assignment after his doctor cleared him for full-time (but not overtime) work, although he was also permitted to make routine traffic stops while on his daily commute.

After co-workers reported some concerns about Koessel's behavior, the Sheriff placed him on administrative leave again and ordered him to undergo an independent medical evaluation by a neurologist. The neurologist found that he would be physically able to work from a neurological standpoint, but recommended that Koessel be examined by a psychologist as there were potential problems with his cognitive functioning that may have resulted from the stroke. The psychologist found that some of Koessel's symptoms could interfere with the performance of his patrol officer duties, specifically his mild to moderate fatigue and episodes of lightheadedness and weeping.

Koessel returned to work as a temporary assistant to the Emergency Management Coordinator, who was housed in the Sheriff's office. Additional funding for the temporary position was not approved and Koessel was ultimately terminated, as he was unable to perform the duties of the Sheriff's Office and there were no other available positions for which he was medically cleared to perform. Koessel did not file a request for a hearing to dispute his termination.

More than a year later, however, Koessel sued the Sheriff's Office, the Sheriff and other defendants alleging violations of the ADA, breach of contract and violations of his procedural and substantive due process rights under the Fifth and Fourteenth Amendments to the US Constitution. The district court granted the defendants' motion for summary judgment, finding Koessel failed to make out a prima facie case under the ADA because he could not show he could perform his job with or without a reasonable accommodation. Specifically, the court found Koessel failed to contradict the psychologist's report that his non-physical symptoms could prevent him from performing his job. The court also granted summary judgment to the defendants on Koessel other claims. Koessel appealed.

On May 14, 2013, the US Court of Appeals for the Tenth Circuit issued an opinion affirming the district court's opinion and holding that Koessel failed to demonstrate he could still perform the essential functions of his job.

To make out a prima facie case of discrimination under the ADA, a plaintiff must show he:

The Tenth Circuit found the second issue was dispositive of the case, and did not reach the first or third elements of Koessel's ADA claim.

Relying on the psychologist's report, which recommended that Koessel be placed in a low-stress position that did not require frequent contact with the public, the defendants claimed that Koessel's impairments interfered with at least three essential job functions:

Koessel agreed that these were essential job functions, but claimed he was able to perform them because:

The Tenth Circuit found that these factors only showed Koessel was physically able to perform his job, and not that he could cope psychologically with high-stress situations. In addition, the fact that the neurologist did not find anything physically wrong with Koessel did not contradict the psychologist's finding that Koessel's psychological issues could interfere with his ability to perform his job.

The Tenth Circuit also dismissed Koessel's arguments that his claim should proceed despite the psychologist's report, finding:

In addition, the Tenth Circuit found that the defendants did not fail to provide Koessel with a reasonable accommodation. Koessel did not request a modification of his job duties, but claimed he did request reassignment to another job after he learned he would not be returning to his patrol officer position. Although employers have a duty to reassign such employees, typically they are only required to reassign them to existing vacant positions, and the employee bears the burden of identifying a specific position. Koessel failed to identify such a position, and although he claimed the County assigned him to the position with the Emergency Management Coordinator and then cut the funding for it, evidence in the record showed this was only a temporary position to begin with.

The Tenth Circuit also upheld the district court's grant of summary judgment on Koessel's breach of contract and due process claims.

The Tenth Circuit's decision highlights that even where a plaintiff demonstrates he can physically perform the essential functions of his job, he may be unable to make out an ADA claim if there is evidence that psychological issues may interfere with his ability to perform his job.