San Diego shares the world's busiest border crossing and depend on Mexico for trade and business.
As Mexicans prepare to elect the country's next president on Sunday, San Diegans across the border stand to gain from the results as well.
Enrique Pena-Nieto is the odds-on favorite as the next president of Mexico, with double-digit lead in most polls. His victory would return the PRI (in English, Institutional Revolutionary Party) to power, after a 12-year absence.
The two other candidates are Josefina Vazquez Mota, of the ruling conservative party. She's considered a long-shot, but would be the country's first female president.
The leftist candiate is Andres Manuel Lopez Obrador, who finished second in Mexico's last presidental election.
A big issue in the campaign: violence and deaths, from Mexico's crack-down on drug cartels.
Voters are asking, is Mexico's war on drugs worth the bloodshed?
Voters will also elect a new Congress. One expert says Pena-Nieto will have more power if the PRI also wins the Congress.
"If he has a congress that is also in control of the party, it's a lot easier to get things done -- just like it is sometimes in Washington," said James Clark, Mexico trade expert.
This could help US-Mexico relations, he said.
"What we hope doesn't happen is that we get some kind of accomodation for the drug dealers, and make some peace, but keep those drug dealers. Because in the long run, they'll just get stronger and the drug trade will get even worse," said Ruben Barrales of the San Diego Chamber of Commerce.
The PRI ruled Mexico for over 70 years, before middle class voters in the National Action Party defeated the party's presidential candidate in 2000.
But many of those same voters now seem ready to return the PRI to power.
They hope it will invigorate Mexico's sluggish economy.