Political Insider's Cicero has a good, short eulogy of the Chuck Hagel for President movement:
As an outspoken antiwar Republican, Hagel was winning some early support from members of his party who were tired of the Iraq conflict and who admired his independence. In some polls in 2006, Hagel polled as high as five percent in a wide GOP field. All of this changed on March 12. Hagel's people made a lot of noise about an upcoming big announcement, and speculation ran high. Was Hagel going to seek the GOP nomination? Would he bolt and run as an independent? Would he quit politics altogether? In the year's most anticlimactic political moment so far, the man famed for his decisiveness and courage said… he hadn't decided.
This instantly deflated much of the tough-guy rationale for Hagel, who then saw others like Fred Thompson steal his thunder. Hagel has not even managed to hit one percent in any national GOP poll in months.
Thompson's actually making the same mistake with what could end up being five months of dithering and "testing the water," but it's a good point. I think Hagel's buzz and chances died away when Rep. Ron Paul started making an impact in the race. When Hagel made his Hamlet speech Paul was running the sort of small fringe campaign everyone expected him to run. Once Hagel hung himself and Paul had his confrontation with Giuliani, the small-but-hardy population of anti-war Republicans stopped shopping around: Paul's fundraising and organizing ramped up. And it's been a bottom-up, grassroots kind of campaign unlike the dour messianic campaign Hagel looked like he was going to make.