This is a fundamental diffreence between the Parliamentary and Presidential system. Why you keep forcing your European on your perceptions of how the American system works despite the number of Americans who have come on here to explain otherwise is beyond me.I remember an ill scenario, which is related to the first quote in this post.. The prime minister of Norway for 8 years.. He was from the smallest party in a coalition of 3 or 4 parties.
Nobody actually knew when they voted, which coalition would be the winning one, nor that he would be prime minister. However, he has dedicated his life to the party and only became the party leader after several decades going through the ranks of the party, a small party.