A federal judge indicated Tuesday that he won’t order President Donald Trump to immediately stop work on the massive new White House ballroom.

But US District Judge Richard Leon left open the possibility that he could intervene in the high-stakes legal fight over the project at a later time.

For now, Leon said, the nation’s top historic preservation group that sued over the project hadn’t shown how it was being irreparably harmed by the construction in a way that required immediate court intervention.

But Leon, an appointee of former President George W. Bush, warned that underground work set to be completed in coming months must not dictate the ballroom’s eventual size or shape while the early stages of the legal challenge unfold.

If it does, he said, it would have to be taken down.

Justice Department lawyer Adam Gustafson was unable to say if it was possible or likely that pouring concrete below ground would dictate the building’s eventual height or width.

“I’m not an engineer,” Gustafson said, adding that nothing suggested it would be impossible to change. He said repeatedly that the ballroom’s design is still “in progress” and the plans have “not been finalized.”

The National Trust for Historic Preservation sued last week over the sprawling, privately funded project, claiming the White House has been unlawfully carrying out the construction because Trump hasn’t gotten approval from Congress or submitted his plans to the National Capital Planning Commission and the Commission of Fine Arts for review, which would give the public a chance to weigh in.

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The group asked Leon to issue an emergency court order that would pause any further work on the ballroom until Congress authorizes it, the commissions review it and relevant environmental assessments are completed.