I'll leave the strategic implications of tonight's outcome to the professional speculators on television. But, as a supporter of progressive causes, I'm struck by how different this feels from the 2004 Iowa race -- when the late implosion of the front-runner (Howard Dean) handed the contest to a candidate (John Kerry) whom almost everybody understood to be a severely limited politician and about whom almost nobody was actually enthusiastic.

You can't say that about what just transpired. Barack Obama has a great many people excited about his candidacy – many of them new to the political process or, at least, new to the Democratic Party. He won this race not because the caucus-goers found him the least objectionable alternative, but because they found him the most appealing. They liked his speeches. They liked his ideas. They liked him

It's been at least two election cycles since the Democrats had anybody like that at the top of their ticket -- two election cycles in which, not coincidentally, Republicans won the presidency.  Whatever his flaws, Obama has always been the Democratic candidate with the greatest political potential, the only one with the ability to transform the landscape.  And tonight he may have begun to do just that.

--Jonathan Cohn