His poll numbers shrinking, shrinking, shrinking, Chris Christie announces his candidacy for President

First of all, you're probably not surprised to learn that there have been 67 Presidential primary polls since December 2012.

And secondly, it's obvious that Chris Christie peaked early -- in November 2013, to be exact.  Guess what started to get big play in the national media shortly thereafter?  (Note 1/8/2014 on the timeline.)

But I don't think this was the only hazard to take the air out of his tires on his road to the Presidency.

Source:  Real Clear Politics

Chris Christie Announces Run, Pledging ‘Truth’ About Nation’s Woes.  (The New York Times, 6/30/2015)

In sum.

Mr. Christie, whose dazzling rise as a national Republican in his first term was matched only by his spectacular loss of stature at home in his second, entered the presidential race bearing little resemblance to the candidate he once expected to be.