Donald Trump has conceded his own administration’s renovation of the Lincoln Memorial reflecting pool was rushed and shoddy, while insisting that alleged vandals were to blame for damage to the Washington landmark.

In a post on his Truth Social platform, the US president said the pool’s contractor had cut some corners to finish the $14m repainting project in time for a 4 July opening. “As with many jobs, there was also some contractor error done by rushing the job,” he wrote on Sunday, claiming the resulting damage from this was confined to “a very small area” and “relatively inconsequential”.

The admission came in a post in which Trump renewed his claim that wider damage to the pool’s blue coating was the work of vandals. He cited legal testimony from an unnamed US National Park Service (NPS) employee – whom he described only as a “highly credible witness”, but did not identify – presented as an eyewitness account. They allegedly saw the former Olympic canoeist David Hearn tearing at the pool’s lining.

“There was substantial other damage to the Reflecting Pool, also but, unfortunately, there is no video or proof, other than the damage, itself,” said Trump. “Security cameras have been, and are being, installed,” he added.

Trump was infuriated when Jeanine Pirro, the US attorney for the District of Columbia, a former Fox News host and longtime loyalist of the president, moved last month to drop criminal charges against Hearn and several other defendants accused of vandalizing the site.

Pirro’s office told the court it had come to believe the damage stemmed largely from a botched, hurried installation by the contractor, Atlantic Industrial Coatings, rather than deliberate sabotage.

Trump reacted angrily, telling reporters he “disagreed 100%” with his own appointee and complaining that she had “folded like a cheap umbrella”. He mused that “I think she choked” on the case, and has since called on Pirro to “re-visit her hastily made decision”, while sparking questions over her future in the job by declining to say whether he would seek her removal.

The US interior secretary, Doug Burgum, who oversees the NPS, joined the Trump pile-on on Pirro, writing on social media that his department had supplied prosecutors with expert and eyewitness testimony documenting vandalism. Pirro’s office has disputed that account, saying prosecutors had only limited information when Hearn was indicted on 2 July and later obtained records about problems with the pool’s installation that undermined the government’s vandalism case.

Hearn’s lawyers rejected the vandalism narrative entirely, saying the case against their client collapsed because it was baseless, and that they are considering further legal action.

The pool, drained and repainted “American flag blue” as part of a beautification push tied to America’s 250th anniversary celebrations, has remained fenced off since the damage was discovered, with officials saying it will not reopen before 10 September. Trump has frequently floated other explanations for the pool’s problems, including algae blooms he attributed to fertilizer and an alleged slit in the lining that he estimated was about 300ft long, and blamed on vandals wielding a box cutter.

The renovation was awarded without competitive bidding, with the Department of the Interior citing the urgency of the anniversary deadline, and its cost has since climbed from an initial estimate of under $2m to more than $16m.

But the pool’s revamp is still under way. “We are working on the Pool, and it will reopen shortly,” Trump wrote over the weekend.