Speaking at a North Carolina campaign rally, Mr Trump said it took only 15 minutes and "we got him" after federal authorities shot and killed Michael Reinoehl, self-described as “100 per cent Antifa all the way”.
After saying that Democrats were attempting to "incite anti-American riots" in the streets, Mr Trump said that the federal government could control the violence within 25 minutes if they were invited in.
"We want to go to Portland so bad, that one would take 15 minutes to set, 15 minutes, and the man that shot another innocent man, this was an innocent man shot, killed instantly killed," Mr Trump said.
"I said what happened: 'well we haven't arrested him'. Two days, three days went by. We sent in the US marshals, took 15 minutes it was over, 15 minutes it was over, we got him. They knew who he was, they didn't want to arrest him, and 15 minutes that ended."
Mr Reinoehl was shot with 37 rounds on 3 September as US Marshals attempted to arrest him over the fatal shooting of Patriot Prayer member Aaron J Danielson in a standoff that has come under heavy scrutiny.
While a handgun was found in Mr Reinoehl's pocket after the shooting, there are conflicting reports from officers and eyewitnesses at the scene, who told The New York Times they didn't hear officers identify themselves or issue commands.
The president has previously bragged about the fatal shooting of Mr Reinoehl, calling the killing retribution for the death of Mr Danielson in Portland on 29 August.
"He shot him, cold blood, two and a half days went by and I put out, when are you going to go out and go get him," Mr Trump said.
“And the US Marshals went in to get, and, in a short period of time, they ended up in a gunfight. This guy was a violent criminal, and the US Marshals killed him. And I will tell you something, that’s the way it has to be. There has to be retribution when you have a crime like this."