Skeptics pummeled Bernie Sanders this week for proposing sweeping policies that defy political realities, but almost nothing compares to his approach on immigration.

Some 9 million undocumented immigrants would gain health care under the Democratic presidential candidate’s single-payer plan, senior policy adviser for the Sanders campaign Warren Gunnels said. But before that could happen, Sanders must first nearly double the number of immigrants given executive relief from deportation. Then he would pass comprehensive immigration reform. By the time Sanders would implement his “Medicare for All” plan, Gunnels said, millions of immigrants would already be on a pathway to citizenship.

Sanders might as well be asking for a purple unicorn, too.

It’s clear that the Vermont senator’s message of sparking a political revolution is resonating where it matters. It helps explain how he could make such significant gains against party front-runner Hillary Clinton’s lead and how, in a matter of a few short weeks, the idea of a Sanders presidency sounds much less like a moonshot.

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But the substance of his proposals easily crumble under scrutiny. Revamping an entire political system isn’t like playing a game of Jenga – if you stack one near-impossible feat on top of another, then if a single piece is removed, the entire tower is certain to topple.

That’s how the most bold and progressive stance on immigration seen yet loses its luster when it’s predicated on a series of steps that would take a political miracle to actually pull off.

“It’s going to take a political revolution to pass single-payer for all Americans,” Gunnels admitted. Close video Sanders soars ahead of Clinton in new poll Think Hillary Clinton and the Democratic establishment are getting nervous about Bernie Sanders? You’re right…. Think Hillary Clinton and the Democratic establishment are getting nervous about Bernie Sanders? You’re right…. share tweet email Embed

Even before Sanders tries to replace all private insurance with a single government-run plan, he faces stacked odds in getting the first of his proposals checked off — that within the first 100 days in office, Sanders would dramatically expand on President Obama’s executive action on immigration.

Obama’s executive measures, known as DACA and DAPA, are already poised to give temporary work permits and deportation protections to nearly 5 million undocumented immigrants. Sanders hopes to see that number swell to roughly 9 million.

The problem is that DACA and DAPA have been frozen under legal challenges for nearly a year. That’s even after Obama very pointedly limited the scope of the programs, heeding legal advice against taking a “significant departure” from what Congress had implicitly approved in the past. The administration’s best hope is that six months from now the Supreme Court will side with its appeal and let the programs move forward before Obama leaves office.

Now this is an issue that snarls all Democratic hopefuls. Clinton and Martin O’Malley too have all pledged to dramatically expand the pool of applicants in similar terms. But it’s almost certain to face challenges in the courts.

Next comes comprehensive immigration reform. Sanders’ plan is light on the exact details but, in essence, he would provide a road map to citizenship for all 11 million undocumented immigrants currently in the U.S. and revamp the visa process for newcomers.

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It’s worth noting that Congress has tried and failed to pass comprehensive immigration reform a number of times over the last decade. Obama vowed to make it happen in his first term, but wasn’t able to pull it off, even while Democrats controlled Congress. (Obamacare, instead, had already sucked all political will out of the room.)

There is virtually no hope that Congress would revisit the reform bill that passed the Senate in 2013. And there are few chances that the Republican-controlled Congress would take up the issue aside from a handful of piecemeal deals that focus on border security and enforcement. A number of immigration advocates have all but given up on seeing comprehensive immigration reform realized until years from now.

After all this comes single-payer health care for all — including immigrants.

“We would hope that by that time that we would have already provided a pathway to citizenship,” Gunnels said.

Setting aside the issues with Sanders’ plan to model a system for everyone off of Medicare, what he’s proposing for immigrants is profound. That’s because, as of right now, immigrants don’t have many health care options.

Undocumented immigrants were very explicitly left out of Obamacare. Recipients must be able to prove legal residency in order to sign up and they receive no federal subsidies. This means that undocumented immigrants aren’t able to buy into the system, even if they’re employed.

The only widespread option is emergency room care for those who qualify for Medicaid. That can be wildly expensive and doesn’t treat the underlying conditions that might have brought them to the ER in the first place.

This was an incredibly contentious issue back when Obamacare was being debated in 2010. Recall the infamous outburst when Republican Rep. Joe Wilson interrupted Obama by yelling “You lie!” That was after the president promised in a major speech on health care that undocumented immigrants wouldn’t qualify for benefits.

This gets to the heart of the political realities of the situation. That the Republican’s presidential front-runner’s platform is to deport all 11 million undocumented immigrants shows where the party generally stands on the issue.

Sanders is probably well-aware of the financial limitations and political pitfalls that can kill a visionary proposal. After all he’s served in Congress for more than two and a half decades.

But immigrant communities have heard a lot of empty promises over the years. Unless the political winds change over the next year, or Sanders refines his plan, this is just stacking one promise on top of another, on top of another.