Attorney General Jeff Sessions on Wednesday warned migrants from the "caravan" that traveled through Mexico last month not to cross into the US illegally.

Though the migrants are applying for asylum — a legally protected process — Sessions suggested that the migrants were "stampeding" the border and crossing illegally.

He said migrants should "wait their turn" and immigrate legally. But for many of those migrants, legally seeking asylum is their only option.

Dozens of migrants from the "caravan" that traveled through Mexico last month have now set foot on American soil and begun applying for asylum, despite the Trump administration's best efforts to deter them.

President Donald Trump has railed against the caravan for weeks, tweeting that the migrants were "defying our borders" and "had better be stopped" before crossing into the US.

Attorney General Jeff Sessions even announced on Wednesday that the Justice Department would send dozens of prosecutors and immigration judges to the US-Mexico border, in part because of the caravan. He accused the migrants of "stampeding" the border, and suggested they were illegally crossing into the US.

But so far, the roughly 200 migrants in the caravan have been waiting outside the San Ysidro port of entry, waiting for a chance to apply for asylum — a process legally protected under current domestic and international law.

Sessions nevertheless told migrants to "make your claim to enter America in the lawful way and wait your turn."

But the asylum-seeking process is a legal one that can only take place once a migrant is already on US soil. Nevertheless, Sessions urged the migrants to apply for legal immigration status before showing up at a port of entry.

"We want the world to know, and particularly our friends in the south, in central America and Mexico and other countries — we want them to know that we have a generous legal system for immigration," he said. "We admit 1.1 million people lawfully every year, and those people should wait their turn."

Sessions did not clarify what visas he believed the migrants should have applied for, but immigration advocates have long sought to highlight how impossible it can be to navigate the US immigration system. For many would-be immigrants, there is no "turn" they can wait for, and no line to stand in.

America's immigration system is designed to only admit newcomers who fall into very specific categories. If someone falls outside those cases, as many central American migrants do, lawful immigration will be challenging, if not impossible.

Here are the many pathways and roadblocks to lawful immigration:

It should be noted that the immigration process for asylum-seekers and refugees are a whole other matter — refugees, for instance, don't necessarily choose to come to the US. The United Nations High Commissioner for Refugees determines which countries they are placed in.

Asylum-seekers, like the caravan migrants, typically do choose the US, but they'll be deported if they can't prove they have a credible fear of facing persecution or torture in their home countries. The Trump administration has already indicated they believe many of the caravan members will be unable to prove their claims of credible fear.

So for people who can't prove a credible fear of torture or persecution, who don't have immediate family members in the US, and who don't have an employer willing to embark on an expensive and lengthy green card application process, the immigration pathways are limited and difficult to navigate.