US Supreme Court allows construction on Trump's $400m White House ballroom to continue
The US president has said the ballroom will be "the greatest of its kind ever built."
The US Supreme Court has allowed Trump's administration to continue construction of his White House ballroom complex.
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In a 5-4 ruling, the court granted the administration's request to block a lower court's order halting above-ground construction of the $400 million ballroom, while a lawsuit by a historic preservation group seeking to stop the project proceeds.
The nonprofit National Trust for Historic Preservation sued last year after the administration tore down the White House East Wing and began building a 90,000-square-foot ballroom without seeking specific approval from Congress.
Mr Trump has said the ballroom will be "the greatest of its kind ever built."
The court wrote on Monday that the plaintiffs lacked the necessary legal standing to sue.
They also said the government would likely suffer "irreparable harm" if the project were blocked, citing national security concerns.
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Monday's ruling, lauded by Mr Trump, was powered by five of the court's six conservative justices.
Chief Justice John Roberts was the only conservative justice to dissent, joined by the court's three liberal justices.
The ballroom construction is "likely unlawful," Roberts wrote, noting that Congress has "plenary constitutional authority over the District of Columbia and federal property" and that it has prohibited structures from being built on federal government grounds in Washington, D.C., without its authorisation.
"The ballroom is a building or structure being erected on federal park grounds - President's Park - in the District of Columbia. Yet Congress has not passed any law resembling 'express authority' for the Executive's construction of it," Roberts wrote.
Writing on Truth Social, Mr Trump welcomed the ruling and called the legal challenge baseless.
"I am pleased to report that the United States Supreme Court has just ruled in favor of the Ballroom/Military Complex being built without any further contingency, doubt, or threat.
"We are living in the Golden Age of America, and this Building will be one of the Greatest ever constructed in Washington, D.C.," the president wrote.
The project combines the above-ground ballroom with an extensive underground complex.
Mr Trump has said the project includes bomb shelters, medical facilities, shielding from drones and missiles and other security features that are "all tied together as one big, expensive and very complex unit."
Construction continues on the lower levels of the ballroom structure, with walls and floors visible.
Brent Leggs, president and CEO of the National Trust for Historic Preservation, expressed disappointment with the court's ruling.
Leggs said the dissent written by Roberts "reiterated what we have maintained from the start of our case - that construction of the White House ballroom is unlawful."
Leggs urged the Supreme Court to fast-track the Trump administration's expected formal appeal, vowing that his group will "continue to advocate with our partners on behalf of the American people, the democratic values of our nation and the preservation of our country's most historically significant places".
In an August 14 Supreme Court filing, Justice Department lawyers echoed Mr Trump's contention that the project is a security necessity, citing assassination attempts against the president and other recent threats.
"This case involves an extraordinary and unlawful injunction that will halt the ongoing construction of the integrated military complex, including a totally secure ballroom space, at the East Wing of the White House, which is vitally required by national security," they wrote.