Donald Trump's immigration proposals are running into some gloomy forecasts at his own alma mater.
Trump has said he would deport all 11 million undocumented workers in the United States.
"We're going to keep the families together, but they have to go," Trump told "Meet the Press" a year ago in an interview.
A new forecasting tool at the Wharton School at the University of Pennsylvania estimates Trump's plan to deport undocumented workers would result in four million lost jobs by 2030.
"A lot of undocumented workers are taking on jobs that frankly no one else wants, so it's unlikely those jobs are going to be filled," says Kent Smetters, an economics professor at Wharton who led a team that took a year to create the forecasting tool by using census data.
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Smetters and his team forecast that if there were no policy changes, the U.S. employed population would total about 160 million workers by the year 2030.
But if Trump, who graduated from Wharton in 1968, were to deport about 10% of undocumented immigrants per year, there would only 156 million workers by 2030. That's based on the maximum number of undocumented workers Trump would realistically be able to deport while in office.
Hillary Clinton's immigration proposals fare better than Trump's in the Wharton tool, but they wouldn't change things much. She's suggested creating a pathway to citizenship for undocumented workers and increasing visa programs for skilled workers.
Wharton's predicts the U.S. would lose about 400,000 jobs by 2030 under Clinton's immigration policy. Smetters says that by making undocumented workers legal citizens, they gain access to safety nets like unemployment insurance and would therefore be a little less inclined to work.
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However, he also points out that documented workers tend to be more productive than undocumented workers. So, while the labor force would be a bit smaller, more workers would earn higher wages and the economy would grow more than it would under Trump.
The rub is that Clinton's policy proposals aren't that different from the current status quo, nor would the job gains be.
"Trump's [immigration] approach is a much bigger negative," says Smetters. "The impact on the economy in the Clinton model is essentially a wash."
Immigration reform is a key factor to job gains, economists say. Hillary Clinton likes to tout an analysis of her economic plan by Moody's Analytics. The Moody's report emphasizes that many of the job gains hinge on immigration reform. (The author, economist Mark Zandi, also donated to Clinton's campaign).
Zandi told CNNMoney that Clinton's economic plan would create 6.1 million jobs by 2026. Of those, 4.7 million jobs are due to her immigration policy -- 77% of the total gains.
Other experts say it's difficult to predict job gains without more specific details from the candidates. So far, Trump's immigration ideas aren't sitting well with economists.
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"If Trump's policies were implemented on immigration...in terms of the economics effects, it would be devastatingly bad," says Joel Prakken, an economist and managing director at Macroeconomic Advisers, a forecasting firm in St. Louis.
Prakken argues Trump's immigration policies would shrink the labor force, weigh down growth and fumble an opportunity to create a visa program that would meet the needs of U.S. companies short on skilled workers.
The debate with Clinton's policies is that some believe she would add millions more jobs than would be gained under current policies, while other economists don't see her moving the needle much on jobs and growth.
Still, when considering either candidates' ability to add jobs, look no further than immigration policy, experts say.
"The principle difference in employment between the two candidates centers around immigration assumptions," says Prakken. "Most of the benefit from Clinton in terms of employment comes from immigration."
