GEOFF BENNETT: Earlier this month, a pandemic era rule that allowed for the quick expulsion of migrants at the Southern border known as Title 42 officially expired.

It marked a major shift in immigration policy and is creating ripple effects on both sides of the border, though not necessarily what many expected.

Amna is at the border now -- Amna.

AMNA NAWAZ: Geoff, here in Brownsville, Texas, authorities and organizations were preparing for a surge in migrant arrivals after the end of Title 42.

But that never happened.

So we visited both sides of the border to better understand why that is.

Under a hot morning sun...

So, how often do you make this crossing?

PRISCILLA ORTA, Lawyer For Good Government: Three times a week.

AMNA NAWAZ: ... immigration attorney Priscilla Orta makes her commute from one nation to another.

It's not even 10:00 in the morning.

It's already about 85 degrees.

PRISCILLA ORTA: At least.

AMNA NAWAZ: And there's about 50 or 60 people already lined up to get into the U.S.

In Matamoros, Mexico, a crowd is already waiting for her.

PRISCILLA ORTA (through translator): How many people are from Central America, from Honduras, from Cuba?

AMNA NAWAZ: Mostly, she's here to clear up growing confusion over who is allowed to enter the U.S. and how.

PRISCILLA ORTA: I have been doing this for 12 years, and even I'm confused.

AMNA NAWAZ: Do you have a clear sense of what kind of guidance to offer them when they ask questions?

PRISCILLA ORTA: No.

And so I'm relying upon the old lawyer's trick of, I'm going to tell you the worst thing that can happen and prepare you for the worst thing.

AMNA NAWAZ: That confusion is based on a matrix of new immigration rules.

As Title 42 ended, the U.S. opened up some legal pathways, but closed others, requiring migrants to schedule an asylum interview appointment through a new app called CBP One, barring them from seeking protection in the U.S. if they didn't first seek it in a country they passed through, and banning entry for five years for anyone caught trying to cross illegally.

They also agreed to take in 30,000 migrants a month from Venezuela, Cuba, Haiti, and Nicaragua, but asked Mexico to take in the same number turned away at the border.

WOMAN: I'm out here at the gateway port of entry, where we are about to return up to 100 Venezuelan migrants back into Mexico.

AMNA NAWAZ: Border crossings dropped from 10,000 a day before Title 42 was lifted to just over 4,000 a day after.

PRISCILLA ORTA (through translator): You have to wait for an appointment if you want something guaranteed.

AMNA NAWAZ: Thirty-one-year-old Carlos says he's trying.

He left Honduras eight months ago, citing police violence, and has been in Matamoros for three.

He says, every day, he logs into the app to try and get an appointment, but can't.

Three months every single day.

CARLOS, Migrant: Every day.

AMNA NAWAZ: Thirty-year-old Glennis and her 7-year-old daughter, Mariangel, have been in Matamoros six weeks after a two-month, treacherous journey from Venezuela.

GLENNIS, Venezuela Migrant (through translator): It wasn't easy, for example, as a mother, to bring my child on the journey, because she cried and said: "Mommy, why are we passing through here?"

But we didn't have any other options.

We don't have a visa or a valid passport.

AMNA NAWAZ: Gladys Canas has been running a Mexican immigration nonprofit here for 12 years.

She says the longer vulnerable populations are forced to wait, the more vulnerable they become.

GLADYS CANAS, Ayudandoles a Triunfar (through translator): As soon as they enter Mexico, migrants face different risks, detention, extortion, abuse, humiliation, loss of life, rape, human rights violations.

Matamoros isn't prepared to receive this number of people.

There isn't infrastructure.

There aren't resources.

There isn't food.

AMNA NAWAZ: As thousands more wait in Mexico to try and enter the U.S. legally, makeshift camps have ballooned in recent weeks.

We're heading now to one of the encampments that's popped up in Matamoros.

There are many.

Some people have been staying in them for months.

And, actually, we have been told there's a lot of communicable diseases, a lot of T.B., a lot of COVID, so we're going to be masking while we're there.

This sprawling complex of tarp tents and blanket shelters houses mostly Venezuelans.

There are other camps further away housing Haitians, Cubans, and more.

Here, the desperation of waiting boils over.

WOMAN (through translator): I just need you to help me.

AMNA NAWAZ: Conditions here are just really appalling.

It is impossible to describe how striking it is.

We are just a few hundreds yards from the U.S. border right now, and this is a sprawling complex now of temporary tents and housing, some 2,500 people, we're told, who are here.

And this isn't even the biggest encampment in Matamoros.

Across the border in Brownsville, Texas, Pastor Carlos Navarro has been stockpiling supplies and prepping beds at his church since well before Title 42 ended.

REV.

CARLOS NAVARRO, West Brownsville Baptist Church: Before May 11, it was real busy.

But, after that, on May 11, after seeing 1,200 people a day, we -- the next, day we only saw 25, and the next day about 40.

AMNA NAWAZ: He says the city is receiving about a few hundred a day now, but he believes they could handle many more.

REV.

CARLOS NAVARRO: Sometimes, we try to forget our roots.

Most of the people came here to the States in the same condition, and they needed help.

So, it's just a matter of empathy.

AMNA NAWAZ: But not everyone agrees.

Former Republican Congresswoman Mayra Flores represented Brownsville for five months until this year.

FMR.

REP. MAYRA FLORES (R-TX): The laws are still not being enforced.

AMNA NAWAZ: Flores, who was born in Mexico to an American parent, wants to see more restrictions at the border.

FMR.

REP. MAYRA FLORES: Right now, the people that are wanting to come here legally, they're being put to the side for them to wait.

And we're focused on the people that are -- have crossed here illegally.

And it's not fair for those people.

AMNA NAWAZ: The U.S. government would say the app is actually a legal process, right?

Those people are coming here legally.

FMR.

REP. MAYRA FLORES: Well, that is just for these people.

What about the people that have been waiting for 10, 15 years?

I have family members, as we speak right now, that have been waiting for 10, 15 years.

Those people need to be prioritized.

AMNA NAWAZ: The next morning, Glennis and her family begin another day in the camp.

GLENNIS (through translator): The Mexican government has said they'd send us to Mexico City and then back to Venezuela.

But we don't want to go back to Venezuela.

We sold everything we had.

AMNA NAWAZ: She says she can't return home.

And, so far, she's not allowed to move forward.

So, for now, she will continue to wait.

Here in Brownsville, the streets are calm after what some described as chaos in a surge of arrivals earlier this month.

But that calm here tonight does belie a crisis that's unfolding really just across the border -- Geoff.

GEOFF BENNETT: And, Amna, I know you have been talking to U.S. officials about what you found in your reporting, including the frustration among many migrants about this new asylum app.

What are those officials telling you?

AMNA NAWAZ: That's right, Geoff.

Well, look, what we were told by a senior Customs and Border Protection official is that the U.S. is currently processing about 1,300 or 1,400 people a day total across the U.S. border.

About 300 or 400 of those are folks who arrive at ports of entry and are allowed in; 1,000 of those everyday, though, are coming in via that CBP One app, that mobile app that you just mentioned.

We're told half of those 1,000 appointments go to people who have some of the earliest registrations on that app, meaning they registered back in January or February.

The other half are randomly allocated on a day-to-day basis.

Here's what's most striking; 1,000 appointments a day is what they're handing out.

They are seeing 80,000 requests a day from across Central and Northern Mexico for people seeking appointments on the app.

And they tell me that number is steady.

The demand is not dropping.

One of the things to note is, the app is geofenced around Central and Northern Mexico, meaning migrants have already made most of the journey they're going to make towards the U.S. border before they can even access that legal pathway.

So that backup is continuing to build.

The U.S. official says they could add more appointments in the coming weeks.

Most migrants we spoke to said they will wait as long as it takes.

They want to enter the U.S. legally.

But some immigration sources tell us they're concerned that, the longer folks have to wait, the more desperate they become.

And we could see those numbers at the border behind me here start to go up in the weeks ahead -- Geoff.

GEOFF BENNETT: Amna Nawaz in Brownsville, Texas, tonight at the Southern border.

Amna, thank you.