This scenario has been done, but I want to make a thread which really thoroughly discusses the topic. We have enough hindsight of years now to do that.
The 2008 primary was very close, and it all came down to Clinton or Obama. Clinton was the established figure, long assumed to be the heir to the throne, and Obama was the youthful inspiring figure who was running on hope and change. After a hard fought contest, Obama ended up getting the nomination.
What if Hillary Clinton had gotten the nomination in 2008 and won the election as any Democrat was sure to do that year?