The military is one of America's most respected institutions. But that cultural feature of American life is under growing strain.

This is because the army now finds itself on a new - and politically fraught -battlefield: the front-line of America's racial conflict.

I witnessed it again last night at the protest rally outside the White House.

Black activists taunted the soldiers on the barricades, chanting that the army is "on the wrong side of history".

  • 'Some of these soldiers, they don't even want to be out here':

One man played a phone video of George Floyd's arrest and death and showed it to the troops, pleading with the National Guard to switch sides.

One young woman protester, close to tears, demanded that the soldiers protect the people, not the President.

What was crystal clear is that this is politically perilous for the military.

The anger once aimed solely at the police is now being redirected towards the army.

James Mattis has attacked the President over his use of the military in the protest. Credit: PA

The former Defence Secretary James Mattis, who served under Trump, has grasped this and launched a withering attack on the President's use of the military to suppress peaceful anti-racism protests.

He said he had watched events this week "angry and appalled".

Mattis added: "We must reject and hold accountable those in office who would make a mockery of our constitution."

But President Trump dismissed that criticism - tweeting that Mattis is "the world's most overrated general".

  • President Trump: 'I think the nation needs law and order'

Instead, he told a right-wing American TV channel that he is a "Law and Order" leader who will stop "bad people doing bad things".

All four police officers involved in the arrest of Floyd have now been charged. That's a move welcomed by activists.

But they say it is only a beginning.

This campaign for racial justice has momentum. It now needs results.