Now she finds herself locked in a fierce battle with her opponent Barrack Obama. But she's already won several big states and she's got her eye on two important primaries in early March, Texas and Ohio.
With the Democratic nomination in the balance, she remains focused, energized and anything but defeatist.
"Barack Obama's candidacy has undeniably gained momentum over the recent months. Have you grappled with the idea, Senator Clinton, that it could be him and not you?" Katie Couric asked Clinton.
"Well, when you're in the heat of this intense experience, the only way I know how to do it is to believe with all my heart that I'm going to be successful. That's what I get up every day and tell myself. That's what I believe. That's what I think is going to happen. So I don't entertain the other option," Sen. Clinton replied.
"Even in your deepest darkest moments, when you're exhausted, you don't think 'Oh my gosh, I'm going through this, I'm spending so much money, I'm so tired and this could be all for naught?' What if that happens?" Couric asked. "You have to, once in a while, think that. No?"
"No, Katie," Clinton said. "You can't think like that. You have to believe you're going to win."
"Otherwise leave the field and let somebody who has the confidence and the optimism and determination that a leader has to have get on that field instead," she added.
Staying on that field requires stamina, especially when she travels to three or more states in one day.
60 Minutes visited Clinton at her home in Chappaqua, N.Y, on Super Tuesday as she sat through 57 satellite interviews with reporters from across the country, repeatedly stressing her readiness to be president.
"How do you do it? I mean, the satellite interviews, the speeches, the travel, the debates, the schmoozing, the picture taking, 24/7," Couric asked.
"I do it because I really believe in what I'm doing," Clinton said.
"I knew you were gonna say that," Couric remarked.
"Well, but it's true," Clinton said.
"But I'm talking about pure stamina," Couric said.
"Pure stamina. I have a lot of stamina and I have a lot of resilience," the senator said.
Asked if she pops vitamins or drinks a lot of coffee, Clinton said, "I take vitamins. I drink tea, not coffee anymore. I have really stopped drinking diet drinks. Because I found that they gave you a jolt, but they weren't good over the long run. I used to drink a lot of them. I drink tons of water. Just as much water as I can possibly drink."
"My two secrets to staying healthy: wash your hands all the time. And, if you can't, use Purell or one of the sanitizers. And the other is hot peppers. I eat a lot of hot peppers. I for some reason started doing that in 1992, and I swear by it," she added.
Her staff is as sleep deprived as she is, many of them longtime loyal Clintonites, with a war room similar to Bill Clinton's in the 1990s.
Barack Obama wasn't seen as a serious threat to her candidacy, until he started filling large arenas and inspiring voters.
"There are two schools of thought. One is the big, huge, enthusiastic crowds don't necessarily translate totally into votes. The other is this is really a steam engine that is just getting started. This is a movement that's just getting started. And the more he's at it, the bigger it's gonna get," Couric remarked.
"I don't see that," Clinton said. "I think what we saw on Super Tuesday is that people who feel like this country's headed in the wrong direction, are increasingly saying, 'We know who we want to go with. We want someone who, on day one, can walk into the Oval Office, be commander in chief, turn the economy around. Really start solving our problems.' And I think that trumps the excitement factor, which is important. And I am very impressed and really excited that there's so many people, especially young people, who are part of our party because of his campaign. But this is really serious business. And we've got two wars going on. We have an economy slipping into recession. We have people who are hurting and are looking for answers. And I believe my campaign and my candidacy offers that."