Tough talk on illegal immigration has been a signature issue for both Republican presidential contenders Donald Trump and Sen. Ted Cruz – you’d be hard-pressed to find a voter who hasn’t heard of Trump’s proposal to “build a wall” on the U.S.-Mexico border.

But perhaps less well-known are these candidates’ equally damaging and retrograde views on legal immigration, and high-skilled immigration in particular. Both Trump and Cruz – Cruz more so – have been outspoken opponents of the H-1B visa program, which allows U.S. companies to attract and hire high-skilled immigrant workers.

It’s a program that many scholars say has boosted U.S. job creation and entrepreneurship since its creation in 1990. And without it, a new study finds, many of America’s best-known and high-flying startups – including Uber, Credit Karma, SpaceX and the workchat app Slack – would not exist. Nor would the thousands of jobs these companies have created.

According to a new report by the National Foundation for American Policy (NFAP), immigrant entrepreneurs are disproportionately responsible for the birth of so-called “unicorn” companies – startups valued at $1 billion or more. Out of 87 “unicorns” operating in the United States today, NFAP found that more than half (44) had been founded by immigrant entrepreneurs. Together, these 44 companies are worth more than $168 billion and have created an average of 760 jobs apiece.

Uber, for example, was co-founded by a Canadian immigrant and directly employs 900 people as well as more than 162,000 “active drivers” in its network. SpaceX, founded by South African immigrant Elon Musk, employs more than 4,000. Yet “few if any of the billion dollar startup companies with an immigrant founder would have been started in the United States,” the NFAP concludes, had legislation introduced by Cruz and his co-sponsor Sen. Jeff Sessions (R-AL) been in place over the last decade.

Dubbed the “American Jobs First Act,” the Cruz-Sessions bill proposed onerous new requirements on employers and applicants, including a “minimum wage” of $110,000 for every new H-1B worker; a two-year moratorium on visas for any company that dismissed an employee for anything but cause; and a requirement that H-1B applicants with bachelor’s or master’s degrees work for 10 years outside the United States before becoming eligible for a visa. While Cruz and Sessions framed the effort as a “reform” of the program, David North of the Center for Immigration Studies described the proposal as “the most sweeping anti-H-1B legislation to be introduced into Congress” in recent memory.

Many immigrant entrepreneurs begin their careers as international students in the United States. SpaceX founder Musk, for example, earned his bachelor’s degree at the University of Pennsylvania before getting an H-1B visa and heading to Silicon Valley. Adam Neumann, founder of the office-sharing company WeWork, earned his degree at the Bernard Barch College of the City University of New York. Yet if the Cruz-Sessions bill were law, Musk would have been required to leave the country for at least 10 years before returning. SpaceX – if it existed at all – would be a South African company, and it wouldn’t be the United States now leading a shot a landing on Mars.

If there is any aspect of the current H-1B program that needs “reform,” it would be to lift the current cap on visas, which now stands at 65,000. According to the U.S. Customs and Immigration Service, the program reached the limit for 2016 visa issuances in April of last year.

With any luck, the United States hasn’t already turned away the Elon Musk of the future.