Mexico's second presidential debate has started with all four candidates insisting that mutual respect must be the basis for their country's relationship with the administration of U.S. President Donald Trump.

The debate was being held in the border city of Tijuana and focused on issues of foreign policy, immigration and border security.

Polls indicate leftist candidate Andres Manuel Lopez Obrador has a comfortable lead over the remaining three candidates. Many have questioned about how confrontational he would be as president with Trump, but his answer Sunday was the most moderate.

Independent candidate Margarita Zavala dropped out of the race last week after struggling to gain traction. She is a former lawmaker and is married to former President Felipe Calderon,

The national election is scheduled for July 1.