Republican presidential candidate Donald Trump released a detailed immigration plan over the weekend, and the "great, great wall" is just the beginning. (Gillian Brockell/The Washington Post)

The ideas once languished at the edge of Republican politics, confined to think tanks and no-hope bills on Capitol Hill. To solve the problem of illegal immigration, truly drastic measures were necessary: Deport the undocumented en masse. Seize the money they try to send home. Deny citizenship to their U.S.-born children.

Now, all of those ideas have been embraced by Donald Trump, the front-runner in the Republican presidential race, who has followed up weeks of doomsaying about illegal immigrants with a call for an unprecedented crackdown.

On Monday, Trump’s hard turn was already influencing the rest of the GOP field. In Iowa, Wisconsin Gov. Scott Walker also began to call for a wall on the U.S.-Mexico border, echoing a longtime Trump demand. Walker said the separation barrier between Israel and the Palestinian territories is proof that the concept could work here.

Walker also seemed to echo Trump by questioning “birthright citizenship,” the constitutional provision that grants citizenship to anyone born in this country. After a reporter asked if birthright citizenship should be ended, Walker said: “I think that’s something we should — yeah, absolutely, going forward.”

But — in a sign of how quickly Trump has changed the terms of this race — Walker had difficulty clearly articulating where exactly he stands on the issue, wanting to steal some of Trump’s momentum but not quite sure to what extent. He went on to say that if the United States enforces the laws it already has, that alone might take care of the problem.

A debate over harsh immigration measures could mean an even bigger headache for Republican leaders, who are desperate to attract more Latino voters. “If Hispanic Americans hear that the GOP doesn’t want them in the United States, they won’t pay attention to our next sentence,” the party concluded in its “autopsy” of the 2012 presidential election loss.

Trump’s immigration proposals have also redefined his role in the race. Previously, the billionaire sold himself as a seat-of-the-pants dealmaker who didn’t want to tie himself down with specific promises. For weeks, his policy on illegal immigrants was essentially that he would figure something out eventually.

“Some are going to have to go,” Trump said in July, when asked if all 11 million-plus undocumented immigrants would have to be deported. “And some, we’re just going to see what happens.”

Now, however, Trump has committed to a plan that is detailed and ambitious, with none of that trust-me ambiguity. For now it is the only formal plank in his campaign platform; on his Web site, it is the only position listed under the category “Positions.”

“What you have to give to Trump is, whatever way he’s done it, he has pushed this front and center,” said Roy Beck of Numbers­USA, which wants to lower overall U.S. immigration, legal and illegal. The elites of the Republican Party, Beck said, “absolutely did not want this discussed in this debate. And instead it’s front and center. It’s strange, but it is the triumph of the working class of the Republican Party.”

Still, on Monday, even some who supported the ideals of Trump’s plan said they weren’t sure it would actually work. It would require a massive extension of federal authority into maternity wards and Western Union offices, tracing the parentage of children and money to deny illegal immigrants a comfortable spot in U.S. society.

“If we could get 12 million people to leave, why don’t we just do that now? This idea that we’re going to get ’em all to leave, and we’re going to get the good ones back, it’s a fairy tale,” said Mark Krikorian of the Center for Immigration Studies, which seeks to reduce illegal immigration. “It’s just not the way that government could function. It’s dopey. It’s a gimmick.”

The most ambitious idea in Trump’s immigration policy would be to overturn birthright citizenship. That right is rooted in the 14th Amendment and another law passed after the Civil War. Both intended to guarantee citizenship for freed slaves, but it was clear that they would also give immigrants’ children a place in America.

“Will [it] not have the effect of naturalizing the children of Chinese and Gypsies born in this country?” then-Sen. Edgar Cowan (R-Pa.), who opposed the bill, asked in the Senate.

“Undoubtedly,” said Sen. Lyman Trumbull (D-Ill.), who supported it, according to the Congressional Research Service. An 1898 Supreme Court decision, United States vs. Wong Kim Ark, involving the child of Chinese immigrants, confirmed that birth in the United States was enough.

Trump, however, says the policy cannot continue. “This remains the biggest magnet for illegal immigration,” says a policy paper on his Web site.

Beyond Walker, two other Republicans in the 2016 race — former senator Rick Santorum (Pa.) and Louisiana Gov. Bobby Jindal — have expressed support for ending the provision this year. Two others, Sen. Rand Paul (Ky.) and Sen. Lindsey O. Graham (S.C.), have supported it in the past.

But Trump is the front-runner, making his backing especially invigorating for the idea’s long-thwarted proponents on Capitol Hill.

“Trump is strong enough that he can do that,” said Rep. Steve King (R-Iowa), who proposed the Birthright Citizenship Acts of 2011, 2013 and 2015, none of which got out of their subcommittees in the GOP-run House. “He has injected this into the presidential debate, and now the rest of them will have to run to catch up with him on the immigration issue.”

Those who want to end birthright citizenship note that many other industrialized countries do not offer the same guarantee to children born to illegal immigrants. But if a President Trump managed to pass a law on the issue, the Supreme Court might find it unconstitutional. If he wanted to amend the Constitution, he would need ratification by the states — starting a long fight that could alienate the same Hispanic voters the GOP has been trying to court.

Even if it worked, Trump would need to find another way of dealing with children born to illegal immigrants.

“Then you would have 11 million, plus their millions of kids, all of whom would be forever stateless in America — a situation that would just threaten social cohesion,” said Frank Sharry of the pro-immigration group America’s Voice. “It would be a mess of our own making.”

Another controversial Trump idea is the mass deportation of illegal immigrants. His campaign has embraced concepts similar to Mitt Romney’s “self-deportation” plan from the 2012 race: Under tougher enforcement, some immigrants will leave on their own.

If they don’t, Trump has said, he’s willing to round them up and send them home. This part of his plan, for now, is short on details.

“But how do you do that?” CNN’s Dana Bash asked the candidate last month.

“Excuse me,” he said. “We have got to find them.”

“But how?”

“Politicians are not going to find them, because they have no clue,” Trump said. “We will find them. We will get them out.”

It also would not be easy — or cheap.

The American Action Forum, a conservative research organization, estimated that deporting all of the country’s undocumented immigrants would take 20 years and cost between $420 billion and $619 billion. It also found that the move would hurt the economy as workers vanished and would put a vast new strain on the U.S. legal system.

“You need prosecuting attorneys, and you need enough judges and magistrates,” said Thad Bingel, who served as the chief of staff of Customs and Border Protection in the George W. Bush administration.

Trump’s crackdown would also try to stop illegal immigrants from sending money out of the United States, by “impound[ing] all remittance payments derived from illegal wages.” That task could require new checks on those wiring money — which, in turn, could spawn new strategies by immigrants to avoid those checks.

On Monday, former Florida governor Jeb Bush — who has opposed calls to deport all illegal immigrants — rejected Trump’s ideas as impractical, both logistically and politically. “How do you revoke remittances?” he asked. “A plan needs to be grounded in reality.”

“Sure, some of the mechanics, some of the logistics, have major hurdles in front of them,” said Bob Dane of the Federation for American Immigration Reform, which seeks to curtail immigration. Still, Dane said, he applauded Trump for the idea at the core of his proposals: that immigration should serve the security interests and protect the jobs of people already in the United States. “My God, somebody’s espousing a principle.”

Other strategies laid out by Trump seek to lower legal, as well as illegal, immigration.

For one thing, Trump would make it more expensive for U.S. companies to bring in skilled workers on H-1B visas. And he would place a moratorium on new green cards issued to workers abroad, to allow overall immigration levels to “subside to more moderate historical averages,” in the words of Trump’s policy paper.

Those ideas are at odds with many mainstream Republicans, who have sought to increase the number of highly skilled immigrants coming to this country legally. They also clash with a statement Trump himself had been using on the campaign trail — that his “great, great wall” would have a door.

“I don’t mind having a big, beautiful door in that wall so that people can come into this country legally,” Trump said as recently as this month’s Republican debate.

Johnson reported from Des Moines.