President Trump on Sunday said that the attempted security breach by an armed man at the White House correspondents’ dinner underscored why he should be allowed to build a $400 million ballroom equipped with the latest security features on the White House grounds.

“This event would never have happened with the Militarily Top Secret Ballroom currently under construction at the White House,” Mr. Trump wrote in a post on social media on Sunday morning. “It cannot be built fast enough!” He raised the issue again in an interview with Fox News late Sunday morning, talking about the security challenges of the hotel where the shooting occurred.

The proposed ballroom is subject to litigation that has repeatedly slowed the project’s progress — and frustrated the president.

Just over a week ago, a federal judge escalated the legal standoff by ordering a halt to aboveground construction, saying the president appeared intent on skirting a previous order by redefining the ballroom project as a critical national security upgrade.

Judge Richard J. Leon said that adding features like bulletproof windows and other standard security features that exist throughout the White House did not exempt the ballroom project from his directives. “National security is not a blank check to proceed with otherwise unlawful activity,” Judge Leon wrote.

The president’s ballroom plans call for a 90,000 square-foot structure on the former site of the East Wing. He has said it will be paid for by $400 million in private donations, and has declined to list the donors. The Times has identified some of them.

A former real estate developer, Mr. Trump has rushed the construction with little time for public review, and in his post on Sunday he again decried a lawsuit seeking to block it a “ridiculous campaign by “a woman walking her dog, who has absolutely No Standing to bring such a suit.”

The lawsuit, he wrote, “must be dropped, immediately,” and “nothing should be allowed to interfere” with further construction.

He made similar comments about the need for a White House ballroom at a news conference on Saturday night, only hours after he was rushed from the stage at the Washington Hilton by his Secret Service protection team.

There were no metal detectors set up at the entrances to the Hilton on Saturday night, and a secure perimeter was only established closer to the ballroom deeper inside the hotel. A security video posted by Mr. Trump showed the gunman sprinting past the security checkpoint before being captured before he could enter the ballroom.

“It’s not a particularly secure building,” he said of the Hilton, before launching into a familiar pitch for the necessity of his ballroom. “It’s bulletproof glass. We need the ballroom.”