The 12th Amendment revised presidential elections.Prior to the 12th Amendment, the two parties would nominate their presidential candidates (like they still do). However, the winner of the election would become the president, and the loser of the election would become vice president.So, for example, in this last election, Donald Trump would have been president, and Hillary Clinton would have been vice president. Can you see the conflict with that? They would constantly disagree on every issue.The 12 Amendment made it so the presidential nominee and vice presidential nominee run together. So, like things are now, Donald Trump ran with Mike Pence, and Hillary Clinton ran with Tim Kaine.Now, the two heads of the Executive Branch come from the same political party, where they used to come from opposite parties.