The bombast-heavy, detail-light presidential campaign of Donald Trump has entered a new phase — that of releasing a few policy specifics spelling out how he'd govern.

For weeks, the reality star and businessman has led Republican primary polls without any platform details on his website and he's skated when asked about substance.

But in an indication that he intends his presidential run to be more than a mere celebrity stunt, he's hired staff in early primary states and he released his first platform paper Sunday.

Building a wall 

The eight-page paper on immigration threatens the government of Mexico, the business community and millions of families living in the U.S. under uncertain legal status.

It's the kind of stuff that's made him an early favourite in polls of Republican supporters, as yet another survey Sunday showed him with a double-digit lead over his next primary rival.

One section explains how he'd achieve an unlikely feat — build a multibillion-dollar wall across the U.S.'s southern border, and get the Mexican government to pay for it.

'The Mexican government has taken the United States to the cleaners.' - Donald Trump, Republican presidential hopeful

Trump said he'd apply financial pressure until the Mexicans pay up. He said he'd impound cross-border remittance payments linked to illegal wages; hike fees for work visas for Mexican CEOs and diplomats, and potentially even cancel them; and increase fees for border-crossing cards and NAFTA worker visas from Mexico.

"The Mexican government has taken the United States to the cleaners," says the Trump paper. "They are responsible for this problem, and they must help pay to clean it up."

No more automatic citizenship 

The plan goes on like this for eight pages.

He would triple the number of U.S. immigration officers; end jobs visas for foreign students; defund so-called sanctuary cities that shelter undocumented migrants; detain and deport undocumented migrants; suspend the granting of green cards until more unemployed Americans enter the work force; and, in one of its more controversial proposals, end automatic citizenship for babies born in the U.S.

Trump has also said he'd undo President Barack Obama's executive orders, including one that granted residency rights to the children of people who entered the U.S. illegally.

Those actions would affect millions of people.

When pressed in an interview Sunday about the potential turmoil his plan would cause, Trump was unapologetic. He said that after booting people out, he'd subsequently assess applications to let some back in.

"They have to go," Trump told NBC's Meet the Press. "Either we have a country or we don't."

The paper proposes an attitude shift, away from an immigration system that benefits the corporate class but not middle-class Americans: "When politicians talk about 'immigration reform' they mean: amnesty, cheap labour and open borders ... nothing more than a giveaway to the corporate patrons who run both parties. Real immigration reform puts the needs of working people first — not wealthy globetrotting donors."

Campaigning in Iowa

Over the weekend, Trump visited the Iowa state fair where he took kids for a ride on his helicopter, and was followed by selfie-snapping crowds and media crews.

Some reports noted that the campaign has ramped up its on-the-ground presence, with 10 paid staffers already touring the early primary state by bus and potentially putting to rest speculation that the Trump bid might never be anything more than a national news-media phenomenon.

USA-ELECTION/TRUMP

U.S. Republican presidential hopeful Donald Trump eats a pork chop at the Iowa State Fair during a campaign stop in Des Moines on Saturday. (Jim Young/Reuters)

Most serious political pundits say Trump can't win the primary. They point to polls showing that many voters dislike him, and suggest that means his growth will stall before that of less-polarizing candidates.

But he's No. 1 for now.

A Fox News poll released Sunday suggested he had 25 per cent support among potential primary voters with his closest rival, former surgeon Ben Carson, far back at 12 per cent.