But here is the good news for Clinton as she holds her first big campaign-style rally Saturday on New York's Roosevelt Island: She still has maybe the clearest path of any non-incumbent in modern times to winning a party's presidential nomination.

"At this stage, Hillary Clinton is one of the most dominant - if not the most dominant - non-incumbent candidates in presidential primaries since 1980," said John Sides, a political scientist at George Washington University.

That's clear in the polls showing her leading the nearest Democratic competition by 40 to 50 points. (By comparison, her lead over Barack Obama at this same point in the 2008 presidential race was 14 points, according to the June 2007 NBC News/Wall Street Journal poll.)

It's also seen in the endorsements, given that she's already picked up the backing of about two-thirds of sitting Democratic senators. (By early 2008, she had endorsements from just a fifth of sitting Dem senators.)