People gather at the U.S.-Mexico border fence to talk to their relatives in Playas de Tijuana, on the outskirts of Tijuana, northwestern Mexico, on July 3, 2016. (Guillermo Arias/AFP/Getty Images)

Large majorities of Americans and Mexicans living in cities along the U.S.-Mexico border oppose building a wall dividing the two countries, rejecting the proposal that presumptive Republican presidential nominee Donald Trump has made a cornerstone of his campaign, according to a new poll released Monday.

Fully 72 percent of Americans near the southwestern border are against a border wall, along with 86 percent of those living in Mexico’s northernmost cities, the poll found. Majorities of those surveyed also say the tone of the presidential campaign is hurting relations between the United States and Mexico — 59 percent of Americans along the border feel that way, and 69 percent of those in Mexico.

The poll — sponsored by Cronkite News, Univision and the Dallas Morning News — comes with several important caveats. It interviewed people in seven pairs of U.S.-Mexican “sister cities,” and cities in the United States tend to be more liberal-leaning than rural areas, which could mean residents would be more inclined to oppose a border wall. Most of the cities also have overwhelmingly Hispanic populations — for instance, Nogales, Ariz., is 95 percent Hispanic. That could also affect the results, since Latino Americans tend to have more liberal attitudes on immigration issues.

Still, the poll is among the first to provide some insight into how people who would be most affected by a wall feel about idea that helped fuel Trump’s improbable rise to the top of the Republican field. According to a Pew Research Center poll this spring, 62 percent of Americans nationwide opposed building the wall, while 34 percent favored it. The issue divides along partisan lines, with more than 6 in 10 Republicans and Republican-leaning independents supporting the wall in the Pew poll, while more than 8 in 10 Democrats were opposed.

Trump has said he wants to build a massive structure, anywhere from 30 to 55 feet tall, along the 1,954-mile southwestern border to curb illegal immigration and drug smuggling. He says he would force Mexico to pay for it — at a cost of about $8 billion — by threatening to cut off the flow of billions of dollars in payments that immigrants to the United States send home to that country.

Democrats and current and former Mexican leaders have scoffed at the wall proposal, which has been incorporated into the GOP platform at the Republican National Convention that begins Monday. Experts and federal officials say a wall would face major obstacles, including environmental and engineering problems; fights with ranchers and others who don’t want to give up their land; and the huge topographical challenges of the border, which runs through remote desert in Arizona to rugged mountains in New Mexico and, for two-thirds of its length, along rivers.

The U.S. government has already spent more than $7 billion to build what is now about 650 miles of southwestern border fencing — nearly half in Arizona. It cost nearly $5 million per mile in some spots.

Throughout his campaign, Trump has expressed confidence in his ability to erect a wall. “Building a wall is easy, and it can be done inexpensively,” he said in an interview last July with The Washington Post. “It’s not even a difficult project if you know what you’re doing.”

Trump argued that a wall “would be very effective” in deterring illegal migrants. “A wall is better than fencing, and it’s much more powerful,” he said. “It’s more secure. It’s taller.”

In addition to Nogales, the new poll surveyed people in Brownsville, Laredo, Del Rio and El Paso in Texas; Yuma, Ariz.; and San Ysidro, Calif. No questions specifically mentioned Trump. The border wall question asked: “Should the United States of America build a wall between Mexico and the U.S. in an effort to secure the border?’’

In other findings, the poll reported that border city residents have overwhelmingly positive views of those living across the border; 86 percent of U.S. residents said they liked their “neighbors in Mexico,” while 79 percent of Mexicans said the same.

When asked how much their city depends on the sister city across the border, 79 percent of Americans and 69 percent of Mexicans said they were at least somewhat dependent. Large majorities of both Mexican and American resident in border cities also favored a program allowing workers to cross the border and return home freely.

Despite the mutually positive feelings, the poll found widespread concern about crime and drugs and distrust of law enforcement among those living on the Mexican side of the border. A 54 percent majority of those living in Mexican border cities said crime and drugs were the most important issue they face, as did a smaller 18 percent of those in U.S. border cities. And while more than 8 in 10 American border city residents said they trust law enforcement officers in their country, that dropped to barely 2 in 10 among city dwellers in Mexico.

The Cronkite-Univision-Morning News survey was conducted April 29 to May 10 by telephone and through in-person interviews among a sample of 1,427 adults living in cities along the U.S.-Mexico border. A random sample of roughly 100 interviewers were conducted in each city. The data were not weighted to population size.