he has remained steadfast in his determination
he may retain the same steadfastness as President Trump over Greenland
steadfast: If someone is steadfast in something that they are doing, están convencidos de que lo que hacen es correcto y se niegan a cambiarlo o a darse por vencidos. Firme en su propósito, resolución, fe, apego, etc. Inquebrantable en su determinación, fe, adhesión, etc.