President Biden’s floating pier is setting up off Gaza’s coast behind schedule and under fire. The secretary of defense, Lloyd Austin, says what sober observers already know: The mission isn’t safe from Hamas despite Mr. Biden’s pledge that no service members will be at risk.

“I’m directing the U.S. military,” Mr. Biden said in his State of the Union address on March 7, “to lead an emergency mission to establish a temporary pier in the Mediterranean … that can receive large shipments carrying food, water, medicine, and temporary shelters.”

Mr. Biden said, “No U.S. boots will be on the ground.” It was the kind of magical thinking that presidents — some more than others — pepper into the political debate. Beyond the walls of the Beltway, though, events have a stubborn tendency to go off-prompter.

Mr. Biden hopes the pier will quiet criticism from key parts of his coalition, including Arab-Americans, Muslims, and leftist college students opposed to Israel. However, those with a closer view feel the pier is a flashy, overengineered response to the suffering — one that will cost $320 million according to a Pentagon spokeswoman, Sabrina Singh.

CARE International’s vice president of humanitarian affairs, Deepmala Mahla, tells Devex the pier is unnecessary when “hundreds and thousands” of vehicles loaded with “food and other required material” are idling across the border in Egypt. The UN secretary-general, Antonio Guterres, agrees that roads are “the only efficient and effective” solution.

“Up to 1,000 American troops will snap together the floating structure three-to-five miles offshore in the western Mediterranean Sea,” I wrote for the Sun in March. “It will then be moved into position and connected to Gaza by a causeway a third-of-a-mile long.” Someone has “to tether the causeway to land,” not to mention provide security.

In his address, Mr. Biden said, “Israel must also do its part” to ensure the pier’s success. “Israel must allow more aid into Gaza and ensure humanitarian workers aren’t caught in the crossfire.” The line drew applause, although it’s impossible to safeguard anyone in a war zone.

Mr. Austin, at the House Armed Services Committee on Tuesday,  said that “it’s possible” Americans will come under fire. Congressman Matthew Gaetz of Florida asked the secretary if “boots on a pier, connected to the ground, connected to service members shooting into Gaza doesn’t count as ‘boots on the ground.’”

“It does not,” Mr. Austin replied. The distinction proved little comfort Wednesday when the Israeli Defense Forces reported that “terrorist organizations” fired mortars at the pier. The attack came as United Nations officials were touring the area. There were no casualties.

In a statement after the volleys ceased, the Israeli Defense Forces says, “The terrorist organizations continue to systematically harm humanitarian efforts while risking the lives of UN workers while Israel allows the supply of aid to the residents of the Gaza Strip.”

Hamas has a track record of seizing or stopping relief shipments, and they imagine the pier presents an additional threat. “Palestinians fear,” the Cradle reported, that it “will be used to forcibly expel Gaza’s 2.3 million residents by sea, rather than to deliver aid.”

A week after Mr. Biden announced the pier, Senator Blumenthal told Politico that he had “very serious questions about how the construction will be done with the assurance of safety to our troops.” He joined Republican and Democratic colleagues, as well as United Nations officials, in expressing doubts.

On “Face the Nation,” Senator Rubio said he had “real concern” about the pier’s chances for success. He said there’s “reason to believe that any aid that goes in there will be grabbed by Hamas and used for their purposes at the expense of the civilian population.”

Mr. Biden’s pier made for good rhetoric at the State of the Union but expect the challenges to its mission to multiply as it nears completion. Despite semantics, the commander-in-chief has deployed Americans to a war zone against an enemy determined to rain death upon them — and that cares not at all if their boots are on the ground or at sea.