CALEXICO, Calif. — President Donald Trump issued a blunt message to migrants considering heading to the U.S., even for asylum: The nation is full. Turn around.

"Our country is full," Trump told border agents and elected officials. "Can't take you anymore. I'm sorry. Turn around. That’s the way it is."

Trump said Mexico has responded this week to his threat to close the southern border with unprecedented effort to monitor cross-border activity, claiming “they’re now apprehending people by the thousands” at their southern border.

"Mexico over the last four days has done more than they have ever done," Trump said. "In 30 years, they've never done it like they're doing now."

Trump visited California after threatening to close the border over concerns Mexico had not done enough to stem the flow of drugs and illegal immigrants. He reversed himself Thursday and gave the country a year to improve conditions.

Trump's long-promised border wall remains an elusive goal, but he planned to examine an area getting upgraded fencing, something the White House intends as a sign of his continued commitment to the wall.

After talking to border officials, Trump visited a section of the 2.3-mile border fence topped with coils of concertina wire visited recently by Vice President Mike Pence a year ago.

Trump's view of the fence was obstructed by metal shipping containers. On the other side of the border, Mexican police officers, and other onlookers gazed at the inspection.

Officials told Trump the border will have about 450 miles of new and upgraded barriers by the end of next year at a cost of about $8 billion. They also told him the existing manpower is "extremely strained."

He arrived in California at 11:37 a.m. with six current and former members of the U.S. House of Representatives, including Minority Leader Kevin McCarthy, R-Calif. Homeland Security Secretary Kirstjen Nielsen greeted the president on his arrival.

Trump was joined at the border by several members of Congress and sheriff who Trump said looked like they came from "central casting."

Trump said many politicians — "mostly Democrats" — don't come to the border and claimed “we can take you to sections that are so dangerous, you can’t come here.”

Trump touted the progress of construction on upgraded border barrier. The 2.3-mile-long replacement project was the first to be completed fully under Trump's presidency.

A spokeswoman for U.S. Customs and Border Protection said the president's visit would not affect operations at the nearby Calexico West port of entry.

After the border visit, Trump flew to the Los Angeles area for a fundraiser. Trump's motorcade had returned to the Naval Air Facility in El Centro by 3:05 p.m. and Air Force One was moving by 3:11 p.m.

As usual, not everyone welcomed the president.

On Friday morning, a group of more than 100 protesters gathered in downtown Calexico and marched west toward the outlet mall. They called their event the Binational March of Unity.

Chad Cooper, 41, was among the earliest protesters in downtown Calexico. He was a teacher in San Diego and Calexico for 15 years and now works for the teachers' union.

"I’ve never seen a president divide the nation like Donald Trump," he said. "I’d love attention from the federal or state government, but the problems we have here are more about air pollution, polluted water, not the border."

MORE:Air pollution's deadly toll along the U.S.-Mexican border

Cooper said he’d like to see Trump, or any president, clean up the rapidly disappearing Salton Sea and work to lower the asthma rate in Imperial County.

Lifelong Calexico resident Sandra Solano spoke to the economic complexity in a border city.

The 24-year-old said nearly all the customers at the Coach store she works at and half her co-workers live in Mexico. She said customers were purchasing goods yesterday and earlier in the week, because they thought Trump would close the border.

"For him to close the border, it’s really intense for us," she said. "I’m worried for my job."

Another marcher, Holtville resident Susan Massey, said the president “has no concept of the society here and how we are interwoven.” She said she often goes to Mexicali to get her car repaired, to see a dentist and to visit a close friend.

Yuma resident Keith Wood, 80, was among the few visible Trump supporters in the crowd. Wood said he traveled to Calexico "to encourage (Trump) to actually close the wall, just the pedestrian part, not the commerce part."

He said he’d like to see an end to "chain migration," the process of allowing family members to join other, legal immigrants in this country. Wood also wants a merit-based immigration system to replace the current system.

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Trump’s threat about closing the border left even Republicans on Capitol Hill suggesting it would be economically calamitous to do so.

Trump backed off, saying Thursday he was giving Mexico a year to do better. If Mexico fails, his administration will impose tariffs on Mexican-made vehicles, he said.

"I don’t think we’ll ever have to close the border," Trump said Thursday in the Oval Office.