Tim Pawlenty's 2011 Presidential campaign has a similarly singular moment you can point to as the end and it wasn't the Iowa straw poll.
I wrote this on June 8th in response to a PPP poll that showed Pawlenty in double digits for the first time:
This is the best showing for Tim Pawlenty in a national poll so far, going from only 5% on May 10th into the low double digits in three weeks. This rise in his support coincides with his official campaign announcement and subsequent media blitz, so it could be a temporary spike, or it could be upward momentum, we'll have to wait and see.
Four days later, on Fox News, Pawlenty uttered a line perfectly designed to destroy Mitt Romney, "ObamneyCare." It seemed like Tim Pawlenty had finally taken the gloves off and would start attacking the front runner. Not only the front runner, but a candidate who occupied almost the same exact political space as him.
And the very next day is the day his campaign died.