Updated at 6:50 p.m. ET

After violence Saturday night in Portland, Ore., left a man dead, President Trump responded by threatening to take unspecified action in the city.

In one of several tweets Monday morning, Trump said, "Portland is a mess, and it has been for many years. If this joke of a mayor doesn't clean it up, we will go in and do it for them!"

The tweet came after clashes between Trump supporters, who entered the city in a caravan of hundreds of trucks, and Black Lives Matter demonstrators.

Portland police officially identified the man who was killed as Aaron J. Danielson on Monday evening; they are still investigating possible shooters and motives. Danielson reportedly was a supporter of the right-wing group Patriot Prayer.

Trump on Sunday tweeted his support for the pro-Trump activists, calling them "GREAT PATRIOTS."

Portland Mayor Ted Wheeler, a Democrat, on Sunday blamed Trump for the violence. "Do you seriously wonder, Mr. President," he asked, "why this is the first time in decades that America has seen this level of violence? It's you who have created the hate and the division."

Trump has been using violence in Portland; Kenosha, Wis.; and elsewhere as a campaign issue, calling for law and order and falsely accusing Democratic opponent Joe Biden of failing to condemn the actions.

In an event in Pittsburgh on Monday, Biden lambasted the president, saying that Trump "sows chaos rather than providing order."

"[Trump] can't stop the violence because for years he has fomented it," Biden said. "He may believe mouthing the words 'law and order' makes him strong, but his failure to call on his own supporters to stop acting as an armed militia in this country shows you how weak he is."

On Tuesday, Trump plans to visit Kenosha, where Jacob Blake, a Black man, was seriously wounded by police last week. In a subsequent protest, two demonstrators were shot and killed and a third wounded; a 17-year-old has been charged with homicide.

Asked during a Monday press briefing whether he would meet with Blake's family during his Tuesday visit, the president said he would not, citing a wariness of attending a meeting with the family's attorney.

When asked if he condemned the Kenosha shooter's actions, Trump declined to outright denounce him, saying that the gunman's actions appeared to be self defense.

"He was trying to get away from them, I guess, it looks like," Trump said, noting the incident was under investigation."I guess he was in very big trouble. He probably would have been killed."

Wisconsin Gov. Tony Evers has urged Trump not to come to Kenosha, saying, "I am concerned your presence will only hinder our healing."

In a statement, Sen. Ron Johnson, R-Wis., pushed back on Evers.

"It is a sad state of affairs when Governor Evers asks the president of the United States to stay out of Wisconsin," he said. "Throughout this rolling tragedy, I've pleaded for calm but also for political leadership that provides the resolve and manpower to end the rioting and allow the safe reopening of downtown Kenosha."

Johnson said he will welcome Trump on Tuesday.

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