An out of control vehicle is no more dangerous (arguably less) than a vehicle being driven by a person who is aiming to knock over a pedestrian or who is reckless as to whether they will knock over a pedestrian.
The US legal system and case law is very different to the UK. I think that if this went to court it would likely be ruled to be self defence.
A clip from the US TV channel ABC showed the car hitting the ICE agent before or just as he opened fire.
At that moment in time, he had to decide whether he was threatened with imminent deadly force. Deadly force doesn't just mean something that could kill you but also, in a UK context, the equivalent of being threatened with GBH (grievous bodily harm).
People usually think of deadly weapons as involving guns or knives etc, but having a huge American car revving it's engine and driving directly at you certainly counts as a deadly weapon.
People have suggested that he should have moved out of the way. But where? It was an icy road and the front wheels did not have traction at first - the car could have gone anywhere.
From a US perspective, part of any legal case would be was his action reasonable? Would a reasonable and prudent person in those circumstances also come to the same conclusion?
It wouldn't be down to the ICE agent to prove that it was a reasonable belief, it would be down to the prosecution to proof that no reasonable or prudent person in that same situation would come to the same conclusion.
There is also no need to be "perfect", just "reasonable" in his belief that he was about to be run over. So the agent didn't have to be "correct" that he was about to be seriously injured by being run over, just that he "reasonably" believed that he was about to be.
That's rather a high hurdle for any prosecution to overcome.
I think there was something like two or three seconds from the woman revving her engine and moving towards the agent and the three shots being fired.