Congress is just a day away from another government shutdown. But unlike the deficit-fueled fights of yesteryear, today's budget showdown revolves around a seemingly unrelated issue: immigration.

This is the story of how President Trump tossed millions of young immigrants into treacherous political waters and nearly capsized government.

It began back in September, when Trump decided to nix the Deferred Action for Childhood Arrivals (DACA) program that protects children who were brought to the U.S. illegally by their parents. Because former President Barack Obama instituted the DACA protections via executive action, DACA only lived by the good graces of whoever occupied the White House. When Trump decided he wasn't interested in preserving the program, he stipulated a six-month window for Congress to pass a permanent legislative fix.

But four and a half months have now passed, and Trump's March deadline draws near. Congress still hasn't figured out what to do about DACA — if anything, the prognosis has only gotten worse.

This is where the budget comes in.

Desperate for a fix, Democrats are now threatening to hold federal funding hostage in order to pressure Republicans to relent on the program. And despite being in the minority, Democrats actually have the legislative leverage to pull it off because any funding bill would require 60 votes to pass the Senate, meaning the GOP needs at least some of their support.

For Democrats, the pressure to come through on DACA stems from the more diverse and socially liberal base that the Democratic Party has cultivated. Since the immigrants protected by DACA, known as the DREAMers, are arguably the most innocent of any group that could face deportation, given they had no hand in their unlawful arrival to the U.S., these individuals inspire the strongest pro-immigration feelings among liberals.

Meanwhile, the GOP has been overtaken by Trump's administration, with its incipient white nationalism, as well as the president's own explicit and vicious opposition to immigration. Despite occasionally giving lip service to a path to citizenship for the DREAMers, the right wing is plainly uncomfortable with the idea and far more concerned with Trump's border wall and instituting new draconian restrictions to legal immigration.

The collision of those two political opposites has made immigration one of the most hotly contested flashpoints in American politics.

Yet for one brief moment, there was hope. Despite the thorniness of the immigration debate, by last week a small bipartisan group led by Sens. Dick Durbin (D-Ill.) and Lindsey Graham (R-S.C.) had hammered out a fix for DACA. The proposal included disbursing funds for heightened border security, while scrapping the "diversity lottery" in favor of visas to cover individuals from countries with Temporary Protected Status, which is extended to immigrants fleeing natural disasters and other catastrophic events. As for DACA itself, recipients would be able to apply for provisional legal status and eventually for green cards and U.S. citizenship, but they would be barred from sponsoring family members for legal status — a concession to conservatives concerned about "chain migration."

But by the time the senators arrived to 1600 Pennsylvania Ave. to discuss the deal with Trump, a gaggle of ultra-conservative Congress members had apparently convinced the president to change his mind — despite the fact that the deal addressed all of the problems the White House had previously outlined to lawmakers. Instead of a blockbuster immigration deal, the lasting result of the meeting turned out instead to be Trump's infamous dismissal of certain nations of origin as "shithole" countries.

The comment was immediately cast as blatant racism, and it betrayed a kind of class prejudice at the international scale. But at its core, it was an example of Trump's fickleness, and the ease with which his mind can be changed by whomever had his ear last. A lot of observers seem to think that, whatever Trump's toxic bloviations, he'll likely sign any deal that actually gets through Congress.

And therein lies the problem. The hardline right-wingers seem mainly upset that the senators' deal didn't include more funding for border security, and they insist that preventing DACA recipients from sponsoring other family members for legal status doesn't go far enough to prevent chain migration. On the flip side, plenty of liberal groups are furious at the deal as is, including the Congressional Hispanic Caucus, the Congressional Asian Pacific American Caucus, and the Congressional Black Caucus.

So who's at the greatest risk politically?

There are 10 Democratic senators who hail from mostly conservative, mostly white states that Trump won. These lawmakers could pay the biggest price if there's a federal shutdown over immigration, because their constituents aren't as concerned about the plight of young immigrants as the larger Democratic base. At the same time, large swaths of the party — and certainly its major presidential contenders — see real political value in making DACA a hill to die on.

Then there's Trump and the GOP. Government shutdowns aren't the end of the world, but they are a huge inconvenience that leaves certain critical government services stalled and thousands of federal employees on furlough and thus without pay. And when it comes time to point fingers, shutdowns tend to get blamed on the party in power.

With a Democratic wave already seeming likely in the 2018 midterms, and loads of Republicans announcing their retirements, this is a dangerous game for the Republican Party.