"Was this terrorism?" a journalist asked on Tuesday.
"Well, I think the driver of the car is a disgrace to himself, his family and this country," Trump replied, "and that is - you can call it terrorism, you can call it murder, you can call it whatever you want."
At the time of the news conference, the name and ideology of the Charlottesville driver, James Alex Fields Jr., were known. At the time that Trump tweeted about Barcelona, details about the driver had not been released by police, though it is possible that the president was privy to more information than the public.
Islamic State supporters celebrated the Barcelona attack, but the group did not immediately claim responsibility, according to the SITE Intelligence Group, which monitors extremist activity.
Recall that Trump claimed on Tuesday that he likes to be cautious when commenting on a violent incident.
"Before I make a statement, I need the facts," he said. "I don't want to rush into a statement."
By the time Trump tweeted on Thursday (Friday NZ time), Barcelona police had called the attack an act of terrorism. The president's language was consistent with that of other officials.
But Trump balked at following similar guidance on the Charlottesville attack. A day before the president's news conference, Attorney General Jeff Sessions had said in interview with ABC News that "it does meet the definition of domestic terrorism in our statute." Even before that, Trump's national security adviser, H.R. McMaster, had used the terrorism label, as had other Republicans, such as Sen. Ted Cruz (Tex.).
Trump still has not called the Charlottesville attack terrorism. Instead, he has spread blame for the violence to "both sides" - white supremacists and counterprotesters.
The president has spent much of the week mired in controversy over his response to the deadly attack in Charlottesville. The speed with which he attached the terrorism label to what happened in Barcelona was striking, as a point of contrast, and probably won't help his effort to shake that criticism.