People don't always seek their party's nomination because they think they can win. Paul, I think, is too far away from mainstream thought and run of the mill corruption to be able to raise the money to win his party's nomination.
Think of all the people running for the Republican slot, this time and last time. Most of them know they have no chance.
They might just want to influence the debate, and move whoever wins closer to a position that they want.
Or they may be looking for book deals and talk show employment.
Or it might just be a way to enjoy good food for 18 months.
Or maybe they just have a huge ego and like to stand in front of cheering people.
Here's something you didn't mention in your excellent list of motivations: Money
When you're a politician you raise campaign chests, and when you retire, you get to keep those contributions.
So, running for president puts you on the national stage, allows you to raise a lot more money.
For someone like Ron Paul this was a win-win. He secured a nice retirement while getting out there and invigorating a grassroots Libertarian movement and also getting his message-- which I think nobody can dispute he's genuinely passionate about-- out there.
For someone like Rick Santorum, though, it's either to help secure his seat against his next challenger, or just greed...
Think of all the people running for the Republican slot, this time and last time. Most of them know they have no chance.
They might just want to influence the debate, and move whoever wins closer to a position that they want.
Or they may be looking for book deals and talk show employment.
Or it might just be a way to enjoy good food for 18 months.
Or maybe they just have a huge ego and like to stand in front of cheering people.