Billionaire Republican presidential candidate Donald Trump's sprawling new immigration proposal calls for deporting the estimated 11 million people in the U.S. illegally and closes many doors to legal immigration. The plan, released Sunday, was quickly embraced by immigration-wary Republicans—Ann Coulter called it the "greatest political document since the Magna Carta."

Trump's blueprint—premised in part on tropes that have been refuted, such as a link between immigration and higher crime—includes policy prescriptions that are impractical, expensive and may violate NAFTA as well as the U.S. Constitution, according to experts.

Here are four reasons it's unlikely to become a reality.

1. High costs for mass deportation

Though Trump's blueprint doesn't lay out costs, the heart of his proposal involves  rounding up and deporting all undocumented immigrants. "They have to go," he said Sunday on NBC's Meet The Press.

Of course, doing this would be very expensive.

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In 2011, Immigration and Customs Enforcement deputy director Kumar Kibble told Congress it costs $12,500 to deport one person. Multiply that by 11 million and the cost comes to $137.5 billion.

A 2010 estimate by the liberal think tank Center for American Progress puts the cost of deporting all 11 million undocumented people at $200 billion over five years. The conservative pro-immigration group American Action Forum made a similar projection this year, placing the cost of a mass deportation program that also prevents future illegal immigration at $400 billion to $600 billion over a decade.

The Department of Homeland Security's budget in fiscal year 2014 was $60 billion, and it says it has the resources to deport 400,000 people per year.

"We're not going to be deporting 11 million people in any kind of short period of time. It really isn't practical," Mark Krikorian, who runs the Center for Immigration Studies, a group that seeks to reduce the current level of immigration, recently said. "You can't put all the toothpaste back in the tube."

2. Birthright citizenship and the Constitution

Trump came out in favor of ending "birthright citizenship," a proposition that will please many conservatives who say foreigners exploit the policy by coming to the U.S. and having children so that they can become American citizens.

But ending that policy would be "clearly unconstitutional," said UCLA constitutional law professor Adam Winkler.

As the Fourteenth Amendment states: "All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside." In the 1982 case Plyler v. Doe, the Supreme Court held that "no plausible distinction with respect to Fourteenth Amendment 'jurisdiction' can be drawn between resident aliens whose entry into the United States was lawful, and resident aliens whose entry was unlawful."

"To end birthright citizenship would require a constitutional amendment," Winkler said. That requires two-thirds of both chambers of Congress and three-fourths of the states. In other words, it's dead on arrival.

3. NAFTA and the costs of building a wall

Echoing a promise he made when he launched his presidential campaign, Trump proposed Sunday to build a wall on the Southern border and make Mexico pay for it. Mexico, however, says it won't do that. Until it does, Trump says, he'll hike fees for U.S. visas issued to Mexicans, and consider tariffs and foreign aid cuts.

The first problem with Trump's plan is the cost. While annual U.S. aid to Mexico has averaged $233 million over the last five years, completing the wall would cost roughly $3.58 billion if past expenses for the project are any indication.

The second problem is Trump's plans may violate the North American Free Trade Agreement and spark a trade war with the United States' third largest trading partner, said Caitlin Webber a global trade expert with Bloomberg Intelligence.

"A big jump in visa fees that only targets Mexicans would violate NAFTA," Webber said, which eliminated many tariffs between the two neighboring countries. "An arbitrary increase in tariffs on Mexican imports would be a flagrant violation of NAFTA and would undermine critical supply chains for U.S. businesses."

4. A green card 'pause' and current law

Along with a swath of protectionist limits on legal immigration and guest-worker visas, Trump calls for a "pause" in issuing green cards in order to have businesses "hire from the domestic pool of unemployed immigrant and native workers." It's unclear how long the "pause" would last or what would be mandated of businesses, but employers sponsoring a worker for a green card are already required to go through a lengthy process—known as a labor certification—to prove to the government they were unable to find an American worker as qualified for the job.

"It sound like he's saying you have to do that part again," said Gregory Siskind, an immigration lawyer based in Memphis. "Which would be ridiculous."

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