What is the Insurrection Act?

"The Insurrection Act gives U.S. presidents the authority to deploy active duty military to maintain or restore peace in times of crisis."
https://www.history.com/news/insurrection-act-thomas-jefferson-aaron-burr

"According to the Congressional Research Service, it hasn't been invoked since 1992 during the riots in Los Angeles that followed the acquittal of four white police officers in the beating of Rodney King. Now-Attorney General William Barr was actually attorney general back then, too, under former President George H.W. Bush."
https://www.cnn.com/2020/06/01/politics/insurrection-act-trump-protesters/index.html

"Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That in all cases of insurrection, or obstruction to the laws, either of the United States, or of any individual state or territory, where it is lawful for the President of the United States to call forth the militia for the purpose of suppressing such insurrection, or of causing the laws to be duly executed, it shall be lawful for him to employ, for the same purposes, such part of the land or naval force of the United States, as shall be judged necessary, having first observed all the pre-requisites of the law in that respect."
https://www.npr.org/2020/06/01/867467714/what-is-the-insurrection-act-that-trump-is-threatening-to-invoke

"A centuries-old law has been thrust into the national spotlight following the president’s threats to use the military to restore order amid protests over George Floyd’s death."
https://www.usnews.com/news/national-news/articles/2020-06-03/what-is-the-insurrection-act-and-how-could-president-trump-use-it

"President Trump threatened on Monday to use federal forces to quell the protests and violence that have swept the country, a measure that legal experts said would require the use of an 1807 law called the Insurrection Act.

“If a city or state refuses to take the actions necessary to defend the life and property of their residents, then I will deploy the United States military and quickly solve the problem for them,” Mr. Trump said in the Rose Garden."
https://www.nytimes.com/article/insurrection-act.html

"The Insurrection Act can be invoked if there’s an insurrection against state law and a state government requests federal assistance restoring order, says Daniel Hulsebosch, a professor of law at New York University School of Law who specializes in early U.S. legal history.

It can also be invoked if there’s an insurrection against federal law, Hulsebosch continues. Crucially, after the Civil War, Congress added a provision allowing the president to invoke the Act without a state’s permission if the state is failing to protect the Constitutional rights of its citizens."
https://time.com/5846649/insurrection-act-1807-donald-trump/

Legal Security Expert: Trump Has Authority Use Insurrection to Act to Put Down Riots
https://www.breitbart.com/radio/2020/06/01/legal-security-expert-trump-has-authority-use-insurrection-act-to-put-down-riots/