AMNA NAWAZ: One of the most divisive issues in this year's presidential race is immigration.

And on the campaign trail, Vice President Kamala Harris and former President Donald Trump have clashed over how to handle immigration policy.

While federal agents reported nearly 2.5 million migrant encounters at the southern border last year, in the last five months, crossings have plunged.

Our Lisa Desjardins has been covering both candidates' plans.

She joins us now.

Good to see you, Lisa.

LISA DESJARDINS: Good to see you.

AMNA NAWAZ: Let's start with the border and border security specifically.

What do we hear from each campaign in terms of how they would handle this issue?

LISA DESJARDINS: Both Trump and Harris have talked about border security.

And in office, both of them have actually increased border security.

But from there, that's where things diverge.

So let's take a look first at Vice President Kamala Harris and what she wants to do.

She has pointed to a particular Senate bill proposal for what she thinks needs to happen on the border as far as security goes.

Here's what she said in the debate.

KAMALA HARRIS, Vice President of the United States (D) and U.S. Presidential Candidate: The United States Congress, including some of the most conservative members of the United States Senate, came up with a border security bill, which I supported.

And that bill would have put 1,500 more border agents on the border to help those folks who are working there right now overtime trying to do their job.

LISA DESJARDINS: On border security, that means 1,500 Customs and Border Patrol agents, but also hundreds of asylum and other new officers.

She also would like to invest in more detection technology specifically to cut fentanyl smuggled in.

Now, that bill, of course, Amna, is the one that former President Trump personally killed, even though it was getting some bipartisan support.

So what would he do as far as border security is concerned?

Let's take a look at the side-by-side here.

He is not proposing to increase the number of border agents, asylum officers or other personnel.

Instead, he is pledging and stressing that he wants to finish his border wall.

Now, Trump's approach to border security is much more about deportation and deterrence than about the actual physical barriers right now at the border.

AMNA NAWAZ: So tell us more about that.

What are we hearing from the candidates in terms of how they want to handle both migrants who are now attempting to cross the border and also the millions who are already here as undocumented immigrants?

LISA DESJARDINS: That's right.

Let's, in this case, start now with former President Trump, because this is a central part of what he is saying and a central part of the debate, of course.

Former President Trump is centered around the idea of having mass deportations, the largest in history in this country, of millions of undocumented immigrants.

He says this would be done by local police, the National Guard, and possibly by active-duty military, with the possibility of increasing detention centers to hold these individuals.

Now, at the debate, Mr. Trump gave his rationale and raised an unproven, debunked idea that Democrats have caused a border crisis to get votes.

DONALD TRUMP, Former President of the United States (R) and Current U.S. Presidential Candidate: This will be one of the greatest mistakes in history for them to allow -- and I think they probably did it because they think they're going to get votes.

But it's not worth it, because they're destroying the fabric of our country by what they have done.

There's never been anything done like this at all.

They have destroyed the fabric of our country.

LISA DESJARDINS: Now it is not legal, of course, for noncitizens to vote in this country.

And there's no evidence of that happening in large numbers.

Republicans say the problem is it's not tracked well enough, but there really is not that evidence.

As for mass deportations, it isn't clear exactly how that would work.

Trump has indicated that he would have a national dragnet to find undocumented immigrants, perhaps beginning with those who they know are criminals, but how would he find them?

It's unclear.

I spoke with Jennie Murray of the center-right National Immigration Forum about concerns.

JENNIE MURRAY, National Immigration Forum: It's extremely problematic and it's problematic to all folks across the country.

What we're finding is over 75 percent of Americans do not support that type of an approach.

Whether you are conservative or progressive, you likely work alongside someone who might be removed.

LISA DESJARDINS: Murray is someone who pays attention to business concerns and say that kind of dragnet could be a problem for the economy, as I think Laura has reported before.

Now, this is only one of Donald Trump's ideas that I think it's important to highlight, not his only enforcement push.

Now Trump also wants to narrowly scale back asylum and access to asylum in this country, to the degree where it might essentially be closed to most people who seek it.

He also would end refugee resettlement in this country.

His key adviser Stephen Miller says Trump also wants to end DACA.

As our viewers and you know, that's the program for those who are brought here as children, sometimes called dreamers.

Trump has gone back and forth on this program, but his key immigration adviser says he wants to end it.

AMNA NAWAZ: So that's the proposals you pulled together from former President Trump.

What about Vice President Harris?

What are her plans both for undocumented immigrants and also for asylum?

LISA DESJARDINS: Harris has not issued yet a comprehensive immigration plan, but she has said a lot about what she wants to do.

She is opposed, opposed to mass deportations, but she has moved to the right otherwise on this issue.

In 2019, candidate Harris, running for president, then said she thought it should be decriminalized, that people crossing the border, it should not be a criminal offense, but a civil offense.

Now, in the debate, just this week, she said instead that it should be an enforced part of law.

So let's look at exactly what she says she would do.

She says that the border needs to be enforced, that she would make asylum harder, but not as difficult as former President Trump.

She also supports refugee resettlement and she would support a path to citizenship for DACA.

Those on the right say that her ideas fall short of solving the problem.

SIMON HANKINSON, The Heritage Foundation: The Senate bill shows that it does not accomplish really anything in terms of border security or immigration reform.

But, as I said, politically, it's a pretty handy cudgel.

It actually makes the situation worse.

It would lock in about two million illegal crossers a year who would be added to the pile in the sort of limbo that is our immigration asylum processing system.

LISA DESJARDINS: Now, the numbers he mentions assumes this unprecedented level of migration we have now.

We know it's not limited to America.

There is a global migration surge right now.

AMNA NAWAZ: OK, so this is what they're proposing as candidates, right?

You have also been digging into their records, what they have actually done.

What is that show?

LISA DESJARDINS: A couple things.

As President, Donald Trump oversaw 52 miles of new primary border fencing.

He also pushed for a ban on Muslims entering this country.

That was rejected by courts, but he says he still wants to ban many people coming from Muslim countries.

A note on his rhetoric, though, as William in this chair last night pointed out, the words from the Trump and Vance campaign often dehumanize immigrants.

Now, as for Harris, she was appointed to oversee root causes of migration.

Republicans say she was in charge of the border.

No, this was about three countries in Central America.

She did secure $9 billion in aid to help address those root causes of migration.

Her campaign says also that she hasn't been to the border since 2021.

In part, they say she is about substance, not about show.

Regardless, Amna, both of these candidates I think are going to have to talk more about this issue in the next few months.

AMNA NAWAZ: It's a big issue this election year.

Lisa Desjardins, thank you so much.

LISA DESJARDINS: You're welcome.