Four years ago, I was reporting from the southern U.S. border when construction on the border wall was abruptly halted overnight after former President Joe Biden took office. Now, with President Donald Trump starting a second term, I headed back to the Arizona-Mexico border to report on what’s happening at ground zero under Trump 2.0.

As dark fell, I was with Deputy Dan Brennan of the Criminal Interdiction Team in Cochise County, Arizona, when he spotted a rental car from Oregon with travel history – documented through an elaborate tracking system – that seemed suspicious.

It turned out to be two illegal immigrants from Mexico being transported by an alleged smuggler from California.

Brennan described human smuggling as an “ever-present theme.”

“It kind of rose to the level of epidemic in the more recent years, at levels that shocked everybody that had been around a while,” he said. “But it’s never not been present.”

But now change is coming to the beleaguered southern border – the wheels set in motion by Trump, who declared in his inaugural address that “all illegal entry will immediately be halted, and we will begin the process of returning millions and millions of criminal aliens back to the places from which they came.”

Cochise County Sheriff Mark Dannels insists the border wall does help, and he says he looks forward to construction resuming.

Along the border in Cochise County, there are huge stacks of metal – actual pieces of border wall — that were paid for and ready to install four years ago, still unused. 

Dannels says “there’s no reason not to” go ahead and use those materials now that Trump is back in office. President Trump’s declaration of an emergency along the border, lifted by President Biden, sets the wheels back into motion.

In the past two months, some of the border wall parts in Arizona and Texas were being sold off for pennies on the dollar by the Biden administration until local officials discovered that was happening and were able to put a stop to it. 

Rancher Kelly Kimbro also saw that firsthand in recent weeks. She owns the Malpai Ranch along the border, where border wall materials sat for four years.

“My thoughts were that the administration leaving Washington was kind of putting the screws to the administration coming in, because that’s costing you and I a lot of money,” she said. “They started hauling them, and all of a sudden we were seeing semi’s just around the clock, hauling them out.”

Detective Cody Sessary is with the sheriff’s SABRE Team, or Southern Arizona Border Region Enforcement. They use technology from New Mexico to California to catch people who cross the border illegally.

He told me that he's seen an “astronomical” difference at the border between the first four years under Trump and four years under Biden.

“During the Trump administration … the most we would see in a month is maybe 800 to 900 people coming across on our camera system,” he said. “There were months in the Biden administration, we were seeing 8,000 to 9,000. And that’s just on our camera system.”

He said since border enforcement was largely abandoned, roads built to catch drug traffickers crossing here at Montezuma Pass in Arizona have become unusable.

“That was one of the purposes of the Trump administration and building the wall and making those roads, is if an agent needed to respond to that ridge line up there, he could,” Sessary said. “But if an agent today needed to go to the other side of that ridge line from here, it would take him an hour and a half going around the mountain range to get to that other side.”

In this part of Arizona, people who cross the border illegally aren’t trying to be caught and get lost in the system like so many others. Here, they’re smuggling fentanyl and other drugs, and people will evade law enforcement any cost. Killer cartels – now declared foreign terrorist organizations under Trump – have earned mind-boggling profits by moving record amounts of drugs and people across the porous southern border.

Under Trump’s new emergency order – many foresee a fresh start.

“It opens up that funding line,” Dannels said. “It opens up the opportunity, innovation, creativity, to complete the wall, the physical barrier, which does work.”

With border security tightened, the cartels may change their activity, Dannels said.

“They just need to renegotiate what President Trump’s new plans are and how they get around that,” Dannels said. “But now they have a coach on America’s side that’s actually going after them. So it’s a more competitive game.”

The cartels likely charged the two men from Mexico $8,000 each to cross. The alleged smuggler would have gotten $800 per head to deliver them to Phoenix, according to police. He was arrested for the exact same thing last month.

For more on this story, watch "Full Measure with Sharyl Attkisson” Sunday. Attkisson's most recent bestseller is "Follow the Science: How Big Pharma Misleads, Obscures, and Prevails."