Hillary Clinton is running for president. Well, not actively -- at least not yet. But, she's running. Here's five reasons why (and make sure to read my colleague Aaron Blake's incorrect-but-interesting counterargument).

1. She has run before. One of the best predictors of future presidential bids is past presidential bids. (Sidebar: This reality is why NO ONE should be surprised that Joe Biden wants to run in 2016; he has already run for president twice!) All politics has an addictive element to it but nothing is more alluring than the presidential race. Hundreds of people cheering for you at every stop you make, chanting your name, doing everything they can to just be near you. A cadre of advisers and hangers-on. (This isn't always so fun.) Scads of media attention. The sheer exhilaration of competition at the highest levels. It's very, very hard to give that up once you know it's out there. And Clinton knows it's out there -- not to mention the fact that she undoubtedly feels as though she has unfinished business after losing in 2008 despite starting that race as a front-runner. (See below for more on that.)

2. She's the biggest non-incumbent front-runner in modern presidential history. Clinton knows better than almost anyone the fragility of front-runner status in a presidential race. At the same time, she is a considerably bigger favorite in 2016 than she ever was in 2008 -- both because of her increased strengths but also because of the weakness of the field beneath her. In a new Quinnipiac University poll, Clinton took 57 percent to 13 percent for Sen. Elizabeth Warren (Mass.), who continues to insist she isn't running. No one else gets double-digit support. Is it likely that at some point over the next year a poll (or polls) might come out in Iowa, New Hampshire or South Carolina that shows Clinton as less than certain to be the nominee? Absolutely. But there has never been a path as clear as this one for a non-incumbent looking at the presidential race. And it won't ever come along again. Clinton knows that.

3. She has let 1,000 flowers bloom. There's Ready for Hillary. There's Correct the Record. There's Priorities USA.  That trio of groups -- all aimed at Clinton's 2016 bid -- have steadily added former and current confidants of the former secretary of state to their ranks. It's hard to imagine people such as Harold Ickes or Jeremy Bird, Obama's swing state director, signing on to such an effort without some sort of wink from Clinton that, yes, she is going to do this. She could have, at any point in the past few years, shut down all of these groups with an indication --  private or public -- that she wasn't so sure about how she would spend her future days. She didn't. That's telling.

4. Her memoir was blah. Clinton's reflection on her time at the State Department -- "Hard Choices" -- was the book of a politician who is not yet done being a politician.Despite the title, Clinton took very few risks in the re-telling of her time as the nation's top diplomat and, unlike former Cabinet officials such as Leon Panetta and Robert Gates, didn't blow up any of her former colleagues including the man in the Oval Office at the moment. It was written, at least in part, to help shape the narrative of her time at State for the campaign to come. This from David Ignatius's review of "Hard Choices" for The Post: "This is a careful book, written tactically to burnish friendships and avoid making enemies. Perhaps that’s inevitable for an autobiographer who is considering running for president, but there are times when the reader feels he is being 'spun' rather than enlightened." Yup.

5. She wants to redeem herself. Think back on Clinton's life; it has been a relentless series of successes at increasingly high levels, right up until 2008. That loss to Obama is the only real blemish on a resume stocked with accomplishments up the wazoo. For someone as goal-oriented and achievement-focused as Clinton, it's hard to imagine she hasn't spent some decent amount of time thinking about how she could have done things differently in 2008. So, when presented with a golden opportunity to "make things right," how does Clinton not do it? She doesn't not. (Double negative for the win!)