US presidential candidate Joe Biden has accused Donald Trump of being a “weak” and “toxic” leader who has “fomented” violence in the country.
Speaking in the battleground state of Pennsylvania, Mr Biden said the US was facing multiple crises, which “under Donald Trump, keep multiplying”.
The Democrat’s comments came amid sharp tensions between the rival candidates over unrest in US cities.
Mr Trump has made “law and order” a major theme of his campaign.
The two candidates have in recent days been trading insults over clashes in the city of Portland. A man linked to a right-wing group was shot dead there on Saturday, as elsewhere in the city a pro-Trump rally clashed with Black Lives Matter protesters.
Portland has become a flashpoint for demonstrations against police brutality and racism since the police killing of African-American man George Floyd in Minneapolis on 25 May triggered a wave of national and international outrage.
Mr Trump is set to visit the city of Kenosha, Wisconsin, on Tuesday amid anger there over the police shooting of black man Jacob Blake.
A teenager has been charged with killing two protesters during the unrest last week. His lawyers said he would fight the charges on the grounds of self-defence.
In his speech on Monday, Mr Biden said the president “long ago forfeited any moral leadership in this country”.
“He can’t stop the violence – because for years he has fomented it,” he told supporters, adding: “We need justice in America. And we need safety in America. We are facing multiple crises – crises that, under Donald Trump, keep multiplying.”
“Does anyone believe there will be less violence in America if Donald Trump is re-elected?” he asked.
The Democratic candidate also called Mr Trump “an incumbent president who sows chaos rather than provides order”.
“Donald Trump has been a toxic presence on our nation for four years,” he continued. “Poisoning how we talk to one another. Poisoning the way we treat one another. Poisoning the values this nation has always held dear. Poisoning our very democracy.”
Mr Trump has sought to project himself as the law and order candidate in November’s election, painting the Democrats and Mr Biden as soft on crime and on the violence that has sometimes flared at anti-racism protests.
The Biden’s campaign’s main line of attack has thus far been focused on the White House’s handling of the coronavirus pandemic and on the fact that more than 180,000 people in the US have so far died with Covid-19. But Monday’s rare public campaign appearance is being seen as an attempt to fight Mr Trump’s law and order message head-on by directly questioning his record on public safety.
Mr Trump has blamed Portland’s Democratic Mayor Ted Wheeler for unrest in the city, and suggested that he will send in federal forces.
Media reports say a man who calls himself an anti-fascist is being investigated over Saturday’s deadly shooting, while the founder of the right-wing group Patriot Prayer identified the victim as a supporter.
Police have not publicly named the suspect or the victim, or specified whether the shooting was directly linked to the clashes in the city between protesters and Trump supporters.
As he threatened to intervene in Portland, Mr Trump on Monday tweeted that if he “didn’t INSIST on having the National Guard activate and go into Kenosha, Wisconsin, there would be no Kenosha right now.”
Unrest broke out in Kenosha last week after Mr Blake was shot seven times in the back. His lawyers say he has been paralysed by the shooting.
A 17-year-old has been charged with killing two people during the subsequent unrest. Kyle Rittenhouse had told journalists it was “his job” to guard buildings in Kenosha against protesters.
Videos on social media showed a man with a rifle being chased by a crowd before he fell to the ground and appeared to fire at them.
Mr Biden’s visit to Pennsylvania – an important swing state – marked an unusual trip for the Democratic candidate, who has worked mostly from his home since coronavirus began spreading widely in March.
The US president is due to make an address later on Monday.