To stem the tidal wave of illegal immigration engulfing America, the most important first step that Donald Trump can take is to order the Department of Homeland Security to enforce our existing immigration laws.

That is exactly what he promised to do, and not just in numerous speeches. It’s an official policy statement on the Trump/Mike Pence website: “Enforce the immigration laws of the United States and restore the constitutional rule of law upon which America’s prosperity and security depend.”

Moreover, it’s a step that he can take on Jan. 20, as soon as Trump is sworn in as our nation’s 45th president.

Over the last eight years, President Barack Obama continually flouted America’s legal immigration system. He condoned so-called “sanctuary cities,” where local governments defy federal immigration laws. He implemented a “catch-and-release” policy, directing law enforcement officials to let illegal detainees leave custody and slip back into our communities.

He has even released—instead of deported—tens of thousands of illegal immigrants convicted of other crimes, up to and including everything from murder, rape, and drug dealing.

Obama’s utter failure to secure our borders produced a huge influx of illegal immigrants. Some of these individuals pose great risks to both public safety and national security. And collectively this mass of humanity imposes an increasingly unbearable strain on government manpower and the public purse.

The situation has gotten so out of hand that the National Border Patrol Council, which represents nearly 17,000 Border Patrol agents, broke its long-standing policy and endorsed Trump. As its president, Brandon Judd, explained, Obama had “handcuffed” the Border Patrol and is “letting illegal aliens dictate” our immigration policy.

The council recommended a number of steps—such as ending catch-and-release and fixing the visa program (where 40 percent of foreigners overstay their visas)—to correct the problems. Trump incorporated all of those recommendations in his immigration reform plan. He added some other steps, too. They include:

Build a wall on the southern border. Many pundits have derided “The Wall.” But, in fact, Congress authorized it a decade ago in the Secure Fence Act of 2006 but never fully funded it.

With Trump in the White House and the GOP controlling both houses of Congress, there will be no more excuses for not appropriating the money to complete the barrier, which in actual fact will be a wall in some places, and fences or other barriers elsewhere.

Move criminal illegal immigrants out, Day One. Trump would revive joint operations with local, state, and federal law enforcement. The administration has done everything it could to stop states and local jurisdictions from helping enforce immigration law, even suing states like Arizona to keep them from assisting the feds.

End sanctuary cities and “turn off the jobs and benefits magnet.” Since so many illegal immigrants come here for economic reasons, enforcing the federal law that bars employers from hiring illegal immigrants will, without question, lead many to self-deport.

Suspend issuing visas in any country that exports terrorism or lacks adequate screening of visa applicants. In an era of transnational terrorism, it’s just common sense to refuse to accept visas from any country “until proven and effective vetting mechanisms” are in place.

Terminate immediately Obama’s two illegal amnesty programs, imposed by unilateral executive action. Federal courts have already ruled one of these initiatives—the Deferred Action for Parents of Americans and Lawful Permanent Residents (DAPA) program—to be unconstitutional and have ordered the administration not to implement it.

Ensure that other countries take their people back when we order them deported. The Obama administration has made no effort on a diplomatic level to do anything about this. A good example is Cuba. The Castro regime refuses to take back criminals ordered deported by our immigration courts, yet Obama did not even consider making that a condition of U.S. diplomatic recognition of Cuba.

Here’s the bottom line: Candidate Donald Trump outlined a workable, effective, and achievable plan for bringing our illegal immigration and border security problem under control. If President Trump sticks to that plan, he will accomplish what many in Washington have wrongly said can’t be done, and the American people will get confirmation that they picked the right man for the job.

Editor’s Note: This op-ed was originally published in the New York Post.