The US President made the threat in a nationally televised address in the White House Rose Garden. Trump said; 

“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.” 

Though the comment was an apparent reference to the 1807 Insurrection Act which allows presidents to quell lawlessness during emergencies, the presumptive Democratic presidential candidate Joe Biden condemned the US President's threat via a tweet he shared. 

Biden who announced in a campaign statement that he would speak on Tuesday morning in Philadelphia “on the civil unrest facing communities across America", accused the US President of using the American military against the American people. 

He tweeted; 

He's using the American military against the American people. He tear-gassed peaceful protesters and fired rubber bullets. For a photo. For our children, for the very soul of our country, we must defeat him. But I mean it when I say this: we can only do it together.

The 1807 Insurrection Act was most recently used in 1992 amid rioting in Los Angeles after another African-American man, Rodney King was beaten by police.  

Bishop Mariann Budde, the leader of the Episcopal Diocese of Washington has also expressed her disapproval of Trump's threat. She tweeted; 

Tonight President [sic] just used a Bible and a church of my diocese as a backdrop for a message antithetical to the teachings of Jesus and everything that our church stands for. To do so, he sanctioned the use of tear gas by police officers in riot gear to clear the church yard. 

The President did not come to pray; he did not lament the death of George Floyd or acknowledge the collective agony of people of color in our nation. He did not attempt to heal or bring calm to our troubled land.

The Bible teaches us to love God and our neighbor; that all people are beloved children of God; that we are to do justice and love kindness. The President used our sacred text as a symbol of division.

We are followers of Jesus. In no way do we support the President’s incendiary response to a wounded, grieving nation. We stand with those seeking justice for the death of George Floyd through the sacred act of peaceful protest.

Congressman Adam Smith, chairman of the House Armed Services Committee also said in a statement; 

President Trump’s decision to invoke the Insurrection Act, and his inflammatory rhetoric, proves that he cannot lead us through these tumultuous times and unite the country. Instead, he has decided to rely on the use of force to address those who he views as a threat