Donald Trump will mobilize the National Guard in Washington, an exceptional measure for a city he says is "overrun by violent gangs," while the mayor of the American capital denies a rise in crime.

The US president said he would initially deploy 800 National Guard troops to restore "law, order, and public safety" in Washington, recalling the National Guard's mobilization in Los Angeles in June after protests.

These National Guardsmen are military reservists trained to respond to natural disasters, but can also fight abroad. AFP reports.

- Reservists -

The U.S. National Guard is a reserve force of the U.S. Armed Forces. Unlike active-duty military personnel, its members are not mobilized full-time and have other, civilian jobs.

Unlike other branches of the armed forces, the National Guard is organized at the state level. It is present in all 50 U.S. states as well as some territories such as Puerto Rico and Guam.

It is therefore the governor of each state who can mobilize and command this force, except in Washington, a city which enjoys a special status, and whose National Guard depends solely on the president.

But it also happens that the president takes direct control of a state at the request of the local governor, or by exceeding his authority, as Donald Trump did in Los Angeles on June 7, a first since the 1960s.

The U.S. Department of Defense budget authorizes a total of 433,000 National Guardsmen in the country, compared to approximately 1.3 million active-duty personnel.

- Natural disasters, wars, riots -

National Guardsmen are traditionally mobilized in the United States during natural disasters: evacuations, distribution of emergency food, debris cleanup, etc.

But they can also be deployed abroad and integrated into active-duty units for combat. Hundreds of thousands of National Guardsmen have fought in Iraq and Afghanistan.

The Covid-19 pandemic represents the last major deployment of the National Guard. Their logistical assistance was invaluable in setting up field hospitals and transporting medical supplies.

- Repression of demonstrations -

The National Guards are sometimes mobilized during public order disturbances or demonstrations.

Donald Trump had already deployed the National Guard to California in June, against the advice of Democratic Governor Gavin Newsom, claiming he wanted to restore order in Los Angeles after protests against waves of arrests of immigrants by the federal immigration police (ICE).

This has also been the case in the past, although it remains very unusual.

During the Black Lives Matter protests in 2020, more than half of the states deployed the National Guard to maintain order and enforce curfews. This was also the case in Washington, D.C.

Prior to that, National Guardsmen were deployed to Los Angeles in 1992 during riots and looting following the acquittal of police officers accused of beating Rodney King, a Black man.

Dozens of people were killed and thousands injured.

The National Guard was also mobilized several times during the 1950s and 1960s, the era of the civil rights struggle, to protect African-American children going to school, following the Supreme Court's 1954 ruling that segregated public schools were unconstitutional.