The dog proved to be the right medicine, Mr. Ovsishcher said: Mickey woke him from nightmares by sensing something was wrong and barking, settled him down when he was alone and anxious, and even checked up on him "like a registered nurse' when he had a fever.
"Take a look at his face,' Mr. Ovsishcher said, comparing Mickey to Chewbacca, the hairy character in the "Star Wars' series. "You can't stay anxious or angry or whatever. You look at that face and you start laughing.'
But now Mr. Ovsishcher is facing eviction from his three-bedroom co-op at Trump Village in Coney Island, Brooklyn, because the housing complex has a no-dogs policy. He is wrestling with a kind of Sophie's Choice: his home or his dog.
In an interview with Mickey resting quietly at his feet, Mr. Ovsishcher said he would rather give up his home, where he lives with his wife, Galina, and their two children, Philip, 15, and Yaffa, 10.
"I can't get rid of a family member,' said Mr. Ovsishcher, 42, who immigrated from Moscow in 1994 and enlisted in the Army five years later.
"If they asked me which I want to keep, the kids or the apartment, I would keep the kids. Same thing with the dog.'
Mr. Ovsishcher's dilemma opens a window on a conflict that crops up regularly in a city that has an ambivalent attitude toward pets, particularly dogs.
The image of the New Yorker walking a terrier or a poodle along a row of brownstones or near a fire hydrant has become an endearing Hollywood cliché. Yet many buildings strictly ban dogs; others, like those managed by the New York City Housing Authority, have size limits; and some have no-pet leases that are observed mostly in the breach or when neighbors complain.
There are, of course, sometimes valid reasons for complaints that can lead to the removal of dogs, even those needed by people with disabilities, said Cissy Stamm, co-founder of New York Area Assistance Dogs. An ill-mannered dog that barks for hours, has accidents in the elevator or nips at neighbors may lose its right to remain.
Still, said Ms. Stamm, who is aided by an Anatolian shepherd for stress and partial deafness, "The laws are so complicated that very few people understand them.'
Many tenants will not move into a no-dog building; others will try to take advantage of a curious loophole in New York City law: a landlord who learns of a forbidden pet on the premises has three months after the discovery to take legal action, or else the dog is there to stay.
Indeed, several tenants in Mr. Ovsishcher's building said that despite the no-dogs policy, many residents had dogs, possibly because they got through the 90-day period, or because they persuaded the management that the dogs were needed to assist someone who was blind, used a wheelchair or had psychological impairments.
Those interviewed said eviction was too harsh a penalty, even if, like Lisa Tropp, 70, a Ukrainian-born home care attendant who has lived in Trump Village for 15 years, they did not approve of tenants' having dogs.
"Many people have dogs, big dogs,' Ms. Tropp said. "But if he lives here, he should stay here.'
The 90-day loophole is one of the issues in the case against Mr. Ovsishcher. He claims that the building staff has seen him with Mickey since August and that nothing was done to remove him until February, when he received a warning letter. Mr. Ovsishcher then applied to register Mickey with the building as a comfort dog, but he was turned down.
Michael Rosenthal, a lawyer representing Trump Village's Section 4 — part of a complex of seven brick towers built in 1963 and 1964 by Donald J. Trump's father, Fred C. Trump, with support from the state's Mitchell-Lama affordable-housing program — said that exceptions to the no-dogs policy were made for service and comfort dogs, but that the letter Mr. Ovsishcher submitted was from his family doctor and not an expert in post-traumatic stress.
"Unless he can show otherwise, the building's position is that it is not a comfort animal,' Mr. Rosenthal said, adding that the co-op board had been forced to act quickly because under the 90-day rule, if they did not, they would have had no recourse.
Mr. Ovsishcher, who works as a subway repairman, has a letter from a psychiatrist, but said he did not include it with his application because he was told by building staff that a letter from any doctor would suffice.
It is not implausible that a judge who saw the psychiatrist's letter might decide to end the eviction action. But if Mr. Ovsishcher lost, he could have to sell his co-op and leave.
Mr. Ovsishcher spent seven years in the Army, first with NATO troops in Kosovo, and then as a field artillery sergeant in a unit firing 105-millimeter howitzer cannons in the Bagram and Kandahar areas of Afghanistan, where he was often peppered with enemy rocket fire.
"Remember the words of the anthem: ‘rockets' red glare,' ' he said. "I lived that. The rockets were flying all night long, but that flag was still standing.'
His symptoms of post-traumatic stress worsened when he learned that a close friend had been killed by a car bomb in Iraq. In February 2010 he occupied the co-op, having paid $387,500 for it. His wife, a certified public accountant, decided this February to run for the co-op board — around the time the building alerted Mr. Ovsishcher that he could not have a dog — and he said co-op politics might be at play in the eviction effort.
Mr. Ovsishcher's tenant lawyer, Maddy Tarnofsky, has filed a federal housing discrimination complaint on his behalf.
"The heart of this story is that there is a guy who comes to this country and enlists and puts himself in harm's way,' Ms. Tarnofsky said. "He didn't have to do this, and he comes back damaged and they spit on him. A doctor recommends he have a support animal, and for some unknown reason they decide that they're not doing this for him.'
Mr. Rosenthal said he had three pending eviction cases involving animals kept by Trump Village residents.