JOHN YANG: Tomorrow Mexico holds the largest election of its history, nearly 100 million registered voters.

The legacy of outgoing president Andres Manuel Lopez Obrador looms large over the balloting which comes at the time of record levels of gangs and cartel violence.

Ali Rogin looks what's its stake for Mexico and for the United States.

ALI ROGIN: No matter the outcome in Mexico's election this Sunday, the country almost certainly will elect its first woman president.

And voters are hopeful that will bring about change.

CRISTINA ALONSO, Galvez Supporter (through translator): This will be a great step forward because it shows us that we can all do it and that we all have the capacity to move forward, to take a country forward, as other women presidents have done.

ALI ROGIN (voice-over): The leading candidates are Claudia Sheinbaum and Xochitl Galvez.

Polls favor Sheinbaum of the ruling Morena Party.

She's a former Mexico City mayor and protege of the outgoing president, Andres Manuel Lopez Obrador.

Sheinbaum promised to continue the social welfare programs that made Lopez Obrador wildly popular.

CLAUDIA SHEINBAUM, Mexican Presidential Candidate (through translator): This administration's promise to reshape the country is a humanist model, protector of patrimony, better wages and pensions without raising taxes.

ALI ROGIN (voice-over): Trailing her by double digits in the polls is Galvez, a former senator backed by an Alliance of Opposition Parties.

She promises a return to democratic checks and balances that she says have been eroded under the current president.

XOCHITL GALVEZ, Mexican Presidential Candidate (through translator): As president, I will punish the criminals.

Extortion will end.

ALI ROGIN (voice-over): Galvez has been critical of Lopez Obrador's failure to curb the cartel violence gripping the country, a key issue this election cycle.

In the small town of Huitzilac, residents live in a state of constant fear, caught in the crossfire between warring gangs.

ANAHI, Huitzilac President (through translator): When the phone rings, I'm terrified that it will be the school saying, something has happened to my kids.

ALI ROGIN (voice-over): The same fear haunts those seeking public office.

Dozens of local candidates have been killed in the months leading up to the election.

Whoever is elected the new head of state will also inherit a nation grappling with an influx of migrants, shortages of energy and water, and the largest budget deficit since the 1980s.

ALI ROGIN: Joining me to discuss this landmark election is Arturo Sarukhan.

He served as the Mexican ambassador to the United States from 2007 to 2013.

Ambassador, thank you so much for joining us.

Let's start.

Let's talk about these two candidates.

What are they campaigning on?

ARTURO SARUKHAN, Former Mexican Ambassador to the U.S.: Well, the main issue for Mexican voters, the top of mind issue, is public security.

Not only because 33, 34 candidates for elected office have been killed, murdered by organized crime in this current cycle, but because homicide numbers during these six years of the Lopez Obrador administration have skyrocketed.

It's trending down, starting to trend down, but the numbers are still breaking records.

ALI ROGIN: And as we mentioned, Sheinbaum is leading in polls.

She's a protege of Lopez Obrador, also known as AMLO.

What would her presidency look like and what are the chances that she's going to win?

ARTURO SARUKHAN: That's the big question mark.

I think the main issue many Mexicans and international observers are asking is whether she will become her own woman, whether she will be able to wean herself from the shadow of Lopez Obrador, from his ranch in southern Mexico once he leaves office.

She has signaled that she might deviate in some aspects of what has been the Lopez Obrador legacy, but I don't see significant changes in terms of her public policies going forward if she's elected front runner.

But a word of caution, I think polls are going to be what we're seeing in the polls of double digit differences.

I think it's going to be much tighter come tomorrow Sunday, the results could be in the 5 percent difference, and that could trigger challenges both from the losing candidate but also from Lopez Orbrador, because he might argue that the electoral institutions are shaving off votes from his candidate.

ALI ROGIN: Fascinating.

We mentioned that this campaign season has been exceptionally violent.

How has that played into this election?

How has it affected it, especially in those many local races that are taking place?

ARTURO SARUKHAN: Well, we already saw a sign of organized crime muscling its way into local and state political processes in Mexico's 2021 midterm elections.

And then it happened again in two key gubernatorial races on the border with the United States, the state of Tamaulipas, in the state of Guerrero, which is one of the most violent racked states in Mexico.

So the big question mark is A, whether we will see signs of violence on Sunday.

And two, the most important issue is whether organized crime will seek to whip or suppress the vote on behalf of Morena come Sunday.

ALI ROGIN: You talked about national security being an important issue for voters.

What are some of the other animating issues this cycle?

ARTURO SARUKHAN: Obviously, the issue of access to public health because of the evisceration of the Mexican state by Lopez Obrador, a lot of the public health programs have been whittled away.

For example, access to cancer medicines for young kids.

This has been a very pressing issue up and down Mexico.

The issue of jobs in the economy is always a relevant one, particularly when Lopez Obrador, which explains his popularity and the support for Morena is responsible for having raised the minimum wage in Mexico.

And so that's had an important impact in terms of economic perspectives for a very significant number of Mexicans.

ALI ROGIN: Of course, this election comes just a few months before the one that's taking place here in this country.

How will the outcome of these two elections affect U.S.-Mexican relations in the next few years?

ARTURO SARUKHAN: Well, obviously, there's no country more important to the United States than Mexico, and vice versa.

These two countries are joined at the hit for the good, I believe.

But obviously, were the Republican Party that today sees all the roads to the White House going through the border with Mexico, whether it's on immigration, whether it's on drugs, whether it's on the narrative of Mexico as the real national security threat to the United States.

The double dynamic of what happens every twelve years when our two presidential cycles coincides is going to be challenging, particularly if Donald Trump were to return to the White House next year.

ALI ROGIN: And how will the issue of immigration factor into that in particular?

ARTURO SARUKHAN: Well, Lopez Obrador has been weaponizing immigration and his relationship with the United States.

You saw that in December when secretaries Blinken and Mayorkas in the middle of the holidays had to run down to Mexico because Mexico decided to stop deportations, repatriations, particularly Venezuelans, coming into Mexico.

The Mexican government restarted those efforts.

One of the reasons that explains why numbers now on the border have diminished in terms of undocumented immigrants being detained by the border patrol is what Mexico is doing.

But in my view, there is a big question mark out there as to whether Lopez Obrador, who will leave office on October 1st, a full month ahead before Americans go to the polls, decides to open those migration valves to create some -- to exert a bit of pressure on the United States and on President Biden before the election.

ALI ROGIN: A fascinating dynamic to be watching for.

Arturo Sarukhan, former ambassador to the United States, thank you so much for joining us.

ARTURO SARUKHAN: My pleasure.