The sad reality is that opioid overdoses are killing tens of thousands of Americans each year. This national health emergency reaches into every state, city, and town in America.

While much of the public attention is focused on the abuse of prescription drugs such as OxyContin and Vicodin, this class of drugs also includes heroin and synthetic opioids like fentanyl.

Drug cartels operating throughout Latin America have rushed to produce these potentially deadly drugs, utilizing transnational smuggling networks specializing in the movement of drugs, people, weapons, and cash back and forth across our porous southern border. Many of the drugs killing our fellow citizens are being smuggled in from Mexico, through Arizona, and then to other parts of the country.

As a nation, we cannot make serious progress in countering this public health emergency without reasserting American control over our borders.

In 2017, the amount of fentanyl seized at Arizona’s ports of entry on the Mexican border skyrocketed 600% over the year before. Smuggled in car compartments and beneath clothing, nearly 140 pounds of fentanyl were seized at Arizona’s ports—enough deadly doses for 32 million adults.

As Arizona’s Drug Enforcement Administration (DEA) spokeswoman Erica Curry put it: “The drugs that we’ve seized here have an impact on the rest of the United States. Because people are dying in Ohio. They’re dying in New Hampshire. They’re dying all over the East Coast from these blue fentanyl pills.”

And they’re ravaging communities in Arizona, which makes the opioid crisis personal, frustrating, heartbreaking, and infuriating for me. Almost everyone in our country has been touched by this crisis. As a physician and former state senator in a border state, I have seen countless lives ruined by this epidemic.

Our first line of defense against the opioid crisis is border security. The DEA is coping with thousands of opioid border crossings every year. This week, federal investigators in Arizona seized a shipment of 130 pounds of 4-ANPP, a key ingredient in fentanyl, capable of producing 30 million deadly doses of the drug. The shipment was mailed from China to Arizona, after which the materials would be moved into Mexico and turned into fentanyl before being shipped back into the U.S.

To me, this is first and foremost about public health and safety. Multinational drug cartels have taken advantage of corrupt opportunities in Mexico to produce extremely addictive and highly dangerous drugs that are killing thousands and destroying the lives of many more.

I’ve visited the U.S.-Mexico border twice in the past two months and I’ve seen stretches of border completely devoid of security. Some areas are “protected” with a four-strand barbed wire fence, while others have nothing at all.

Effective border security demands a multi-layered approach beginning with a physical wall that serves as a deterrent to drug smugglers, who often traffic drugs across areas of the border that are not patrolled. It also must extend to the effective use of technology, a fully staffed and supported Border Patrol, and ending catch and release policies.

Congress’s persistent failure to appropriate resources to secure our frontier and block cartel access to Americans is costing lives in every state and every congressional district. Border security is no longer a regional issue, but a national one. Together, we must act to protect future potential victims of this public health emergency. We must build the wall.

Kelli Ward is a physician, former state senator, and Republican candidate for the U.S. Senate in Arizona. Follow her on Twitter.