A President can rule within his own country as a tyrant, and behave without as a dithering weakling. It only depends upon the contempt by which he views his own country, the corresponding indifference with which he views its place in the world, and his own personal hubris.
And strength doesn’t mean the use of force. Strength means saying what you mean, meaning what you say, doing what you say you’ll do, and not saying you’ll do things you won’t. Honesty. Morality. Consistency. Like properly raising a child, or training a dog, or sentencing a criminal.