Donald Trump has rocketed to the top of the 2016 Republican primary polls because he has embraced the base's populist fervor on immigration. But his hardline rhetoric aside, is his substantive policy position on the issue really that different from most pro-amnesty Republican candidates?

In an interview with CNN's Dana Bash, Trump suggested that he would deport the bad illegal immigrants but offer "legal status" to the good illegal immigrants. "We got to move 'em out, we're going to move 'em back in if they're really good people," he said.

That's essentially what "comprehensive immigration reform" promises to do: separate illegal immigrants who can't pass a background check from others who will pay back taxes, fines, learn English, pass a civics test and jump through whatever other bureaucratic hoops are supposed to distinguish the path to "legal status" from amnesty.

This type of legislation generally fails because few voters think any of these conditions will actually be enforced in practice. Many conservatives have a word for bills promising to only legalize the "really good people" but enforce immigration laws for everyone else: amnesty.

Even if the already overtaxed immigration bureaucracy was somehow able to process all the applications effectively, you'd be faced with the following dilemma. If a large number of people are denied, many illegal immigrants will prefer to remain "in the shadows" rather than expose themselves to the risk. To eliminate that, you have to be more lax in enforcing the conditions for legalization, bringing you back to the amnesty problem.

Roughly 90 percent of those who applied for legalization under the Immigration Reform and Control Act of 1986 amnesty were approved. It's estimated that comprehensive reform bills like the McCain-Kennedy proposals during George W. Bush's administration and the Gang of Eight would legalize about 85 percent of the illegal aliens already in the country.

Trump can potentially argue he would be much stricter in his criteria and would therefore legalize at a rate much lower than 85-90 percent. But the Republican field is already filled with candidates who claim to be against amnesty while favoring paths to legalization and even citizenship that a large majority of current illegal immigrants could potentially qualify for.

If Trump is the Republican front-runner because he is the pro-enforcement alternative to pro-amnesty candidates, these details are at least as important to work out as how he would get Mexico to pay for the border wall.

(h/t Ed Morrisey)