US protests updates
Mr. Trump said he would send in the military if cities and states failed to solve the problem themselves. "If a city or a state refuses to take the actions that are necessary...then I will deploy the US military" Donald Trump US President.
However, Defence Secretary Mark Esper has said he does not support the use of active troops in the current situation. Some state governors have questioned if the federal government has the authority to send in troops without their permission. There are already thousands of troops deployed from the National Guard, which is a reserve force for the US Army.
However, a US law passed in the 19th Century lays out circumstances when the government in Washington DC can intervene without state authorization. The Insurrection Act says the approval of governors isn't required when the president determines the situation in a state that makes it impossible to enforce US laws, or when citizens' rights are threatened.
The law was passed in 1807 to allow the president to call out a militia to protect against "hostile incursions of the Indians" - and it was subsequently extended to allow for the use of the US military in domestic disturbances and to protect civil rights.
Another law passed in 1878 requires congressional authorization for domestic military use, but a legal expert told the BBC that the Insurrection Act was sufficient legal authority on its own for the president to deploy the army.
It is widely accepted that the president would have legal grounds to employ the military without asking for approval from the states in the current circumstances. "The key point", says Robert Chesney, a University of Texas law professor, "is that the president determines to make; the governors do not have to request his help."
According to the Congressional Research Service, the Insurrection Act has been used dozens of times in the past, although not for almost three decades. It was last invoked in 1992 by former US President George HW Bush during riots in Los Angeles after the governor of California requested federal help.
The law was used throughout the 1950s and 60s during the civil rights era by three different presidents, including when there were objections from state governors. President Dwight Eisenhower faced objections when he used the law in 1957 to send US troops to Arkansas to control a protest at a school, where black and white children were being taught together.
Since the end of the 1960s, the use of the law has been rare. Congress amended it in 2006 following Hurricane Katrina in an attempt to make military assistance more effective, but the amendment was repealed after state governors objected to it.