She could have run simply to steer the debates, and/or to lay groundwork for a future campaign. It's looking to be a boring Democratic primary. I'm sure that there will be plenty of speculation that a such a primary will hurt Clinton's chances, but I doubt it.
She's been telling people that for the last two years. I have mixed feelings. I'd much rather see her as President, but I also think she's less likely to win than a moderate like Hillary. The Presidency is overrated. She's right, senior Senators arguably have more influence.a chance to try and make a difference on things that really matter.
Has Warren ever demonstrated that she would be a good president? She has fairly narrow expertise -- all of which is more useful in Congress. I've seen about 200 articles about Warren running and none about how well she would handle foreign policy and a host of other issues with which she has very little experience. And sure, a president doesn't need to (and can't) be a policy polymath, but Warren is pretty close to single-issue. I thought the left had learned from its (self-pronounced) mistake with Obama, who had no "CEO" background. He was elected because he fit the moment, not because he would be a good president. I think he's turned out fine (different conversation), but many liberals disagree. Elizabeth Warren would never be elected, but if she ran it would be to ... fit the moment. Not because she's qualified. Addressing mk's point -- yes, Warren could raise the stakes, adjust the debate, for Hillary if she ran in the primary. But a) that wouldn't help Hillary's chances in the general, if you care, and b) nothing that is said, promised or discussed in the primary has any bearing on policy after the inauguration.
I hope for a strong competitor for Clinton in the primaries. Clinton has a LOT of baggage, and I don't know if she's really who the Democrats want to field, regardless of the fact that she is, frankly, overqualified to be president with her foreign policy experience.
The thing is, if you're a democrat you've gotta pin your hopes on Clinton. Warren driving Clinton left during the primary directly correlates to her losing votes in the general. If you're more in the middle/don't care category, then that's fine. But diehards may be shooting themselves in the foot asking for Warren.
I think the question needs to be asked - Who else is there? is Clinton THE great white hope of the democratic party?