Billionaire Bill Ackman is calling on President Biden to secure the border as Texas battles with the federal government over its authority to defend itself from illegal border crossings. 

Ackman was responding to a letter from former FBI agents who told leaders in Congress that low security at the border is one of the most “pernicious” threats to Americans.

“Military aged men from across the globe, many from countries or regions not friendly to the United States, are landing in waves on our soil by the thousands,” the former FBI agents wrote. 

TEXAS GOVERNOR DOING ‘EXACTLY RIGHT THING’ AMID CONSTITUTIONAL BATTLE OVER BORDER ENFORCEMENT: LEGAL EXPERTS

“I find the [FBI] agents’ message irrefutable and extremely concerning,” Ackman wrote. “It is shocking that [Biden] is fighting Texas’ attempt to protect our southern border. Why aren’t Federal agents protecting our border rather than fighting to keep the border open to millions of unaccountable masses entering illegally at a time of great geopolitical uncertainty and heightened terrorism risk?”

“How does this make any sense for the safety and security of our country?” he asked. “What is Biden or, perhaps better said, the people behind Biden thinking?”

Ackman also wrote that the debate over the border makes it almost a “certainty” that Biden will “lose the election” in a post on X Friday.

TEXAS SLAMS BIDEN ADMIN, PROMISES TOUGH BORDER MEASURES AFTER SCOTUS RAZOR WIRE RULING  

The latest Supreme Court decision in Texas’ battle with the Biden White House has sparked a showdown over the Lone Star State’s constitutional authority to defend itself with the federal government seemingly getting in its way. 

On Monday, in a 5-4 decision on an emergency appeal, the Supreme Court ruled to temporarily overturn a lower court’s injunction that banned the federal government from cutting razor fencing Texas had installed along the border near Eagle Pass while litigation continues. 

Late Wednesday night, Texas Gov. Greg Abbott declared his constitutional authority to reserve the right of his state to self-defense against an invasion, adding that the executive branch had broken its constitutional pact with the states by failing to enforce federal immigration laws. 

“The federal government has broken the compact between the United States and the States,” Abbott wrote in a public statement. “The Executive Branch of the United States has a constitutional duty to enforce federal laws protecting states, including immigration laws on the books right now. President Biden has refused to enforce those laws and has even violated them.”

Legal experts told Fox News Digital Texas is well within its constitutional rights and within the Supreme Court’s order to keep building the razor-wire fence even if the feds continue to cut it before an appeals court addresses the matter.

Fox News’ Brianna Herlihy contributed to this report.