The backside of Churchill Downs hums with activity as workers clean stalls, bathe horses and lead the muscular animals on strolls to cool them down after workouts. The quiet is broken when they speak to each other and the horses — in Spanish.

Though they do their work a world away from the grandstand and Millionaire's Row, where fans will sip mint juleps, don fancy hats and cheer for their Kentucky Derby favorites on the first Saturday in May, immigrants have become indispensable at Churchill Downs and other tracks, people in the industry say. Now, fear is spreading that a Trump administration crackdown on immigration will be a calamity both for the tracks and for many of their workers.

While there's widespread acknowledgement that some jobs go to undocumented workers, many trainers rely on the H-2B visa program to supply immigrant workers legally, and the tightening of that program has contributed to a worker shortage.

Some argue that the presence of foreign workers has a downward drag on everybody else's income. But Dale Romans, the second-winningest trainer in Churchill's history, says he can't find American workers to do the jobs.

"This is definitely a business that survives on an immigrant workforce," Romans said. "Without it, I don't know what we would do."

The apprehension on the backside has been stoked by the election of Donald Trump, who staked out a role as an immigration hard-liner during the campaign and referred to some Mexican immigrants as rapists and murderers.

"I wouldn't say it's an extreme fear, but there is nervousness" among Churchill's immigrant workers, track chaplain Joseph del Rosario said. "There's fear they're going to get kicked out just because they're not citizens."

Said one 53-year-old backside hand who has worked at racetracks across the country: "I'm scared. Because one day, I don't know, they catch me and send me to Mexico."

The man, who agreed to an interview only on the condition his name not be used because he fears being exposed to immigration authorities, said his visa expired a couple of years ago but he has kept working, moving up the ranks in the barns where he works. His family has made a life in the United States; if he had to return to Mexico, he said, he'd probably toil in the avocado fields.

Even workers here legally on visas worry about the threat of immigration crackdowns.

"A lot of people here, they're scared," said Cesar Abrego, a 46-year-old groom who came from Guatemala on an H-2B visa. "With the president coming, everybody says, 'Be careful.'"

Like many of the immigrant workers, Abrego dutifully sends money back home. He has three children to support, and worries the visa program that sustains his family will be cut. He could find construction or roofing work in Guatemala, but believes his approximately $450-per-week take-home pay as a groom would be cut more than half.

It's a complicated, time-consuming process for horsemen to get visa workers to their barns. Trainers typically hire immigration attorneys to handle the paperwork.

The H-2B program is capped at 66,000 visas per year, and horse racing competes with many other industries for the coveted slots. Applications for the visas far outpace available slots. The crunch worsened when the program's "returning worker" exemption expired last September.

Congress has not reauthorized the exemption, which allowed existing H-2B visa holders to keep returning on the same visas, which weren't counted against the cap. Immigration lawyers and members of horsemen's groups have been meeting with lawmakers in hopes of getting the exemption reinstated.

"The shortage of workers on the backside is severe," said Will Velie, an Oklahoma-based immigration attorney. Trainers unable to secure enough H-2B workers "have a choice between turning away work or breaking the law if they can find people that are here undocumented."

At Barn 4 on the backside of Churchill, Romans' crew was down about 15 workers for the spring racing season at Keeneland in nearby Lexington, as the trainer prepared for the upcoming meet at Churchill. Romans' latest Kentucky Derby contender is J Boys Echo, winner of the Gotham Stakes at Aqueduct.

The staffing shortage was more dire for trainer Gary Patrick, who races mostly at tracks in Indiana and Florida. The 70-year-old Patrick had to wield a pitchfork to clean 20 stalls each morning as he waited for visas to be approved for more immigrant workers he wanted to hire.

"I'm in a trap," said Patrick, who is in his 50th year as a trainer. "I don't have any help and I'm killing myself. It's a bad situation for a trainer to be in. And I'm not the only one."

Patrick has tried to hire local help. He rarely gets a response, and those that show interest don't last long. "Two of them did show up and I got about three days out of them," he said.

Not everyone at the track believes there is no alternative to hiring immigrants. Longtime Churchill backside worker Marc Olinsky sees them as the reason wages aren't higher.

"The trainers hired these guys for nothing, and they ran anybody who earned a salary out of here," Olinsky said, while helping a farrier shoe a horse. "I think immigrant workers that come here legally should do whatever they want to do in this country. And those that are illegal should get put in jail until they're sent home, period."

Velie noted that visa workers are paid above minimum wage. A groom makes about $15 an hour, twice the federal minimum wage, he said.

"The H-2B program isn't used by the horsemen as a way to lower wages or to get around hiring Americans," he said. "It's a vehicle of last resort."

Baldemar Bahena's journey toward the American dream started as a teenager on the backside of tracks. When he left Mexico on a visa, he spoke a little English but had a knack with horses.

More than 30 years later, Bahena oversees dozens of workers as Romans' top assistant. Bahena and his wife became U.S. citizens and they settled into a four-bedroom home in Louisville. Their two teenage children are college bound.

"He's a great American success story," Romans said of his friend.

But Bahena, 49, worries the door of opportunity may be closing behind him for other immigrant workers toiling at racetracks in search of a better life for their families.

"They're good people," he said. "They're working hard all the time. They're kind of scared."

Bahena voted for Trump because of the Republican's business background, and said he holds out hope the new president will make things better.

"I tell everybody, just chill out a little bit and I think in another year or something, it'll be all right," he said. "I think he's going to change his mind because he's a real, real good businessman, and he's going to figure it out that these people are good people."