With a record number of Democrats participating, Sen. Barack Obama won Iowa’s first in the nation presidential caucuses Thursday night by an unexpectedly wide margin.  Sen. Hillary Clinton and former Sen. John Edwards remained deadlocked in a virtual tie for second place.

Although large crowds were a cause of frustration for caucus organizers in all corners of the state, results streamed in steadily and without much incident.  The turnout, which was measured at about 239,000, was greater than almost anyone expected.

This year’s Democratic caucuses were unusual because of how difficult they were to predict — even at the very end.  Although Iowa Independent placed Obama at the top of its final power rankings last week and listed Clinton and Edwards in a virtual tie for second place, few other observers were willing to speculate about the final results.  In truth, it was anybody’s contest to win until the very end.

All six of the major Democratic presidential candidates spent significant time and money in Iowa over the past year.  Clinton, Edwards, and Obama each had hundreds of paid employees fanned out across the state to organize Democrats and left-leaning independent voters.  Sen. Chris Dodd, who finished at the bottom of the pack, took the extraordinary step of moving his family to Iowa for the final months of the campaign.  Sen. Joe Biden frequently mentioned in speeches how crucial Iowa was to his campaign strategy.  And Gov. Bill Richardson and Edwards both visited — and took questions in — all 99 of Iowa’s counties.

Although Edwards was outspent by his two chief rivals by millions of dollars in Iowa, the former North Carolina senator’s presidential hopes were largely tied to a successful finish here.  And Clinton, whose campaign assumed an air of inevitability for much of the campaign, showed her vulnerability.

Both Edwards and Clinton had downplayed expectations in recent days.  Former Gov. Tom Vilsack told a reporter that Clinton had “already succeeded” by making it into the top three here.  Edwards made an effort to showcase his organizations in other early primary states in an effort to demonstrate that his campaign would not end in Iowa no matter the results.

Late Thursday, after most precincts had reported their results, both Clinton and Edwards told gatherings of their supporters that they planned to continue their campaigns in New Hampshire despite the disappointing results.  Biden and Dodd both plan to drop out of the race.