WHAT'S BEEN GOING ON IN PORTLAND?
Protests over the killing of George Floyd by police in Minneapolis have taken place in downtown Portland for more than 50 consecutive days, drawing at times more than 10,000 mostly peaceful demonstrators.
A relatively small number of activists have vandalised downtown buildings, including the federal courthouse, and attacked police and federal agents.
Trump issued an executive order on June 26 to protect monuments and federal property after protesters tried to remove or destroy statues of people considered racist, including a failed attempt to pull down one of Andrew Jackson near the White House.
The Department of Homeland Security dispatched agents to Portland as well as Seattle and Washington, D.C., starting around the Fourth of July weekend.
WHY THE DEPARTMENT OF HOMELAND SECURITY?
DHS, which was formed after the September 11, 2001, attacks to improve the nation's response to the threat of international terrorism, oversees some of the largest US law enforcement agencies.
That includes the Border Patrol as well as Immigration Customs and Enforcement, which are seeing less of their usual activity because of Covid-19.
DHS also oversees the Federal Protective Service, which guards federal buildings along with the US Marshals Service.
DHS sent members of the Border Patrol, along with Secret Service officers, Air Marshals and others, to Portland to protect the downtown courthouse complex.
WHAT HAPPENED AFTER FEDERAL FORCES ARRIVED?
Federal officers and protesters clashed in the streets outside the federal courthouse.
Demonstrators broke windows and did other damage, hurled rocks at the officers and shined lasers in their eyes. Agents have fired tear gas to disperse demonstrators and arrested about 43 people since July 4, mostly for minor offenses.
Tensions escalated after an officer with the Marshals Service fired a less-lethal round at a protester's head on July 11, critically injuring him.
They ratcheted up further when agents in unmarked vehicles with generic "police" patches on their camouflage uniforms arrested people at night without identifying themselves.
DHS officials defended the arrests today, saying they were carried out lawfully and intended to protect officers from violent crowds.
They also noted it is routine to use unmarked vehicles. But it seemed to many like the US had created a secret police force, and it drew lawsuits as well as more protesters into the streets.
IS IT LEGAL FOR FEDERAL FORCES TO BE USED LIKE THIS?
Yes, to a certain extent. Federal authorities can enforce federal laws on federal property, like the courthouse in downtown Portland.
But state and local officials say the federal agents have operated beyond their jurisdiction, and that has raised constitutional issues now being challenged in court.
As Michael Dorf, a professional of constitutional law at Cornell University, told AP: "The idea that there's a threat to a federal courthouse and the federal authorities are going to swoop in and do whatever they want to do without any cooperation and coordination with state and local authorities is extraordinary outside the context of a civil war."
EVEN IF IT'S LEGAL, IS IT A GOOD IDEA?
DHS has assisted with local enforcement before, but not without consent.
It sent agents to Puerto Rico to help confront a spike in crime linked to drug trafficking in 2013 and dispatched the Border Patrol's tactical team to track two escaped convicts in rural upstate New York in 2015. But as John Cohen, a former senior DHS official under Obama and President George W. Bush, noted, those were conducted in close cooperation with state and local authorities.
Employing DHS on its own, in a mission that seems to be suspiciously aligned with the President's re-election campaign, appears to be unprecedented.
"If the public begins to perceive that they are being partisan in how they operate they lose credibility, and if they lose credibility, they lose public trust," said Cohen, who now teaches at Georgetown University.
WHAT CAN BE EXPECTED TO HAPPEN NEXT?
The Oregon attorney-general filed a lawsuit arguing that the federal government had violated the rights of citizens of the state by detaining people without probable cause.
The American Civil Liberties Union has also sued, seeking to stop the federal government's use of rubber bullets, tear gas and acoustic weapons against journalists and other legal observers. These and other legal actions could force the federal agents to change tactics or perhaps downsize their mission in the city.
Acting DHS Secretary Chad Wolf at a news conference urged state and local authorities in Portland to work with the federal government to stop the violence directed at federal personnel and property.
He also sought to draw a sharp distinction between people demonstrating against police brutality and those attacking the courthouse. "If you're looking to peacefully protest in Portland, the department respects your right to do so," he said.
Trump has praised the DHS response and criticised local officials for letting a situation get "out of control."
An official told AP that Homeland Security was planning to deploy about 150 agents to Chicago for at least two months in a mission expected to focus on gun crime, not the protection of federal property.
Trump, who sees the use of federal officers as a way to embarrass Democratic local officials, wants them used in other cities. "We're going to have more federal law enforcement, that I can tell you," Trump said.
- AP
