1. There is a panoply of ambitious Democrats who watched Barack Obama leapfrog them in 2008 and won’t want to miss their opportunity this time around.
2. If Clinton announced on March 1, 2015, there would only be 10 months before the calendar turned to 2016. Given how much her candidacy — or at least her decision-making about her candidacy — has and will continue to freeze the field, there would be a mad scramble for donors, activists and key consultants in early states the likes of which we haven’t seen in modern presidential history.
3. There is no obvious front-runner in a Clinton-less field. Vice President Biden would be the nominal favorite for the nomination, but you could also make a credible case for New York Gov. Andrew Cuomo or Massachusetts Sen. Elizabeth Warren or even New York Sen. Kirsten Gillibrand to occupy that space.
One other impact of Clinton taking a pass on the race: It would strengthen Republicans’ chances of winning the White House while simultaneously changing the nature of the discussion in the GOP primary.