“Everyone knows that walls work,” claimed the president as he addressed reporters outside the White House. “You look at different places, they put up a wall, no problem.
“You look at San Antonio, you look at so many different places; they go from one of the most unsafe cities in the country to one of the safest cities, immediately, immediately. It works. We have to put them up, and we will put them up. We've got to."
Mr Trump’s comments on Saturday were intended to justify his demand for $5.7bn to fund a US-Mexico border wall.
The president may have intended to refer to El Paso, a Texas border city he used as an example in a similar anecdote last week.
“El Paso… was one of the most dangerous cities in the country,” Mr Trump claimed during a 14 January speech in New Orleans. “A wall was put up. It went from being one of the most dangerous cities in the country to one of the safest cities in the country overnight.”
The president’s depiction of El Paso’s transformation is also inaccurate, however.
The city has never been “one of the most dangerous” in the US and already had one of the lowest crime rates among the country’s largest urban areas before construction of a 57-mile border fence began in 2008.
El Paso’s violent crime rate was also lower in each of the three years before the fence was built than in each of the three years after it was finished, according to the Annenberg Public Policy Centre’s fact-checking website.
Mr Trump’s reference to San Antonio’s non-existent wall came before a live televised address in which he offered expanded protections for some undocumented immigrants as a concession to Democrats in return for the $5.6bn.
House speaker Nancy Pelosi and the Democrat Senate minority leader Chuck Schumer rejected the proposed trade-off, which the president had hoped could bring an end to a month-long federal government shutdown.
Ms Pelosi dismissed the offer as “a compilation of several previously rejected initiatives, each of which is unacceptable and in total, do not represent a good faith effort to restore certainty to people’s lives”.