The union representing US Border Patrol agents is on the attack against President Obama for, as they put it, "threatening" agents, claiming that he's trying to force them to implement his executive actions on immigration even after a federal ruling blocking those actions from going into effect.

That's not exactly true. A federal judge blocked the administration's attempt to allow millions of unauthorized immigrants to apply for protection from deportation, but it didn't keep the government from making decisions about who it should and shouldn't deport. In fact, in the wake of the court ruling, federal immigration policy depends on what rank-and-file agents do in a way it never has before. Immigration agents have more power than anyone else in determining who gets deported — and, accordingly, have the responsibility to make sure that's in line with the administration's policy.

the fate of millions of immigrants relies on what agents do in the field

But rank-and-file agents have been fighting the administration for years over attempts from the White House to restrict agents' ability to deport unauthorized immigrants. Now, they're using the court battle as an opportunity to challenge the administration. That raises big questions about who really controls immigration policy — and the power struggle has massive real-world consequences for immigrants who are still struggling under the fear of deportation, despite everything the Obama administration has tried to do to remove that fear.

What the White House sees: making decisions about who should get deported

Shawn Moran, the spokesman for the Border Patrol union, told Fox Newslast week that "Like any other federal employee, (Border Patrol agents) follow policies. And the current policy is that we arrest and deport illegal aliens." But that hasn't actually been federal policy since 2010. The Obama administration's immigration policy is built on the principle of "prosecutorial discretion": that immigration agents should be spending their limited resources on some types of immigrants (like convicted criminals), rather than others (like parents of US citizens). Most recently, when President Obama announced the new deferred-action programs in November 2014 (the ones currently being held up in court), he also issued a memo changing agents' prosecutorial priorities — and making the pool of immigrants who should be getting deported much smaller and more clearly defined.

These policies are different from from the administration's deferred-action programs: the DACA program for young unauthorized immigrants that's been in effect since 2012, and the program for parents of US citizens and green-card holders that was put on hold by the court challenge). Those programs involve giving an immigrant a piece of paper saying he won't be deported for a certain amount of time. The "prosecutorial discretion" policies, on the other hand, are about the decisions that agents make on any given day about who's worth putting into deportation proceedings and who isn't.

And while Judge Andrew Hanen of the Southern District of Texas put the new deferred-action programs on hold in February, his ruling didn't affect the government's policies about when agents should decide not to deport immigrants. In fact, Judge Hanen explicitly wrote in a footnote that "Whether or not (the federal government) may exercise discretion by simply not removing people in individual cases is not before this Court."

So agents' instructions about who not to deport are clearer, and more restrictive, than they've ever been. At the same time, the administration's other attempt to limit deportations, by providing deferred action to immigrants, has been put on hold. So the fate of the millions of immigrants who would be eligible for protection from deportation if the administration wins its court case — or the millions more who aren't eligible for protection, but aren't supposed to be "priorities" either — relies on the actions of agents in the field.

What immigration agents see: attempts to keep them from doing their jobs

If the federal court ruling doesn't mean that unauthorized immigrants should be "arrested and deported" wherever found, why is Moran saying it does? The answer is that for as long as the federal government has been trying to guide immigration agents to limit deportations, agents have resented the restrictions. And now, they're saying that the president is "threatening" them to force them to go along with the program.

Don’t threaten Border Patrol agents over an executive action that a federal judge placed on hold, Mr. President. http://t.co/xkiCPS0XXa — NBPC (@BPUnion) February 26, 2015

The tweet (and Moran's Fox News appearance) are referring to something Obama said during his televised town hall last week. Obama said that rank-and-file immigration agents are being "instructed" to deport certain types of immigrants, and, by implication, not to deport others — and that if they don't follow those instructions, there will be "consequences."

But the union's slightly mischaracterizing what Obama was referring to: this isn't about the policies that have been blocked by a federal judge. But the conflict between the administration and rank-and-file agents is very real, and it's been getting gradually more intense throughout Obama's two terms.

Rank-and-file immigration agents, in both the border and the interior, have long been hostile to the administration's attempts to tell them who they can and can't deport. Immigration agents suffer from some of the lowest morale in the federal government, and union reps generally tie this to a feeling that they're not being allowed to do their jobs by deporting unauthorized immigrants. (It probably doesn't help morale that in recent weeks, agents have been dealing with the threat of a DHS shutdown which would force them to come into work without pay.)

This feeling long predates the president's 2014 executive actions — in fact, it predates any actual policy limiting deportations. The National ICE Council, the union representing ICE agents, issued a vote of no confidence in then-director John Morton in summer 2010 — before any memos had been released attempting to limit deportations.

But for all that agents complain, ICE field offices have demonstrated — especially during Obama's first term — that they didn't have much of a problem deporting immigrants who were supposed to be "low priorities" anyway. And unauthorized immigrants and immigrant-rights activists were hyper-aware that the administration's rhetoric didn't match what was happening to people on the ground.

What immigrants see: the White House can't protect them from its own agents

That's one big reason why the president started using deferred action to protect unauthorized immigrants to begin with: if the goal was to keep immigrants from living under the daily trauma of fearing deportation, relying on immigration agents simply wasn't achieving that goal.

The evidence so far indicates that rank-and-file agents are going along with the president's executive actions from November. But immigrants aren't yet convinced that that's going to last. And comments like Moran's certainly indicate that their fears are justified.

That's why President Obama found himself getting questions from immigrants at last week's town hall about whether their relatives would be safe from ICE. Town hall host Jose Diaz-Balart actually pressed Obama pretty hard on the subject, saying that "where the rubber meets the road," agents have often deported people the White House says aren't getting deported. In response, Obama said that there would be "consequences" for agents who didn't follow instructions.

It's not clear what exactly Obama meant by "consequences." But his November memo that further restricted agents' "priorities" made it clear that agents don't get to make decisions about who to deport on their own. Under the memo, agents are allowed to deport someone who's not a priority — but only if the director of their field office decides it would "serve an important federal interest." (It's clear from the rest of the memo that simply deporting immigrants for being unauthorized does not count, according to DHS, as an important federal interest.)

On that, the Border Patrol union and the president agree: immigration agents are supposed to follow policy, not set it. But that's undermined by the fact that the two don't agree on what the current policy is. The administration's trying to reassure immigrants that they're no longer under the daily threat of deportation, but the tension between the White House and rank-and-file agents raises the question: is that something the administration can even control? And for how long?