According to those involved, the union's board voted Oct. 23 to endorse Sen.. Union president Gary Smith promptly called Obama with the news.
A person familiar with the conversation said it was clear to Obama that the endorsement was a done deal. The person did not want to be named because the conversation was meant to be private.
But the situation changed Tuesday night.
The board, including some new members elected during the weekend, deadlocked 8-to-8 on a motion to endorse Edwards. Smith broke the tie in Edwards' favor.
Obama, campaigning Wednesday in Chicago, hinted at the intrigue.
"There were some interesting aspects of how that whole thing played itself out," Obama told The Associated Press by telephone. "I won't go into all the details of it; maybe you can get some of the background from others.
"We have got some very strong allies in the union, and had received word that the board initially had voted to endorse us. There were some changes to procedure made that we don't entirely understand and I'll leave it up to you guys to sort it all out," Obama said.
Smith ducked questions Wednesday about whether he had promised Obama the endorsement, saying three times that he'd been in touch with several campaigns.
Asked a fourth time whether he had spoken with Obama, Smith snapped: "You can stop asking. That is the answer. It's going to be the consistent answer, no matter how many times you keep asking."
Jay Ward, the union's director, acknowledged the board's 7-to-5 vote on Oct. 23 for Obama. But he said the executive board returned a day later and wanted to reconsider, especially with the union's annual convention scheduled later that week.
In a straw poll at the convention, 50 union members said they were undecided or favored no immediate endorsement. Edwards got 23 votes, Obama 19 and Sen.14.
That didn't sit well with Stephen Foster, a board member until Saturday who considered last week's vote for Obama final.
"The vote was taken and the chair announced that we had a presidential endorsement for Senator Obama. The board then authorized him to call Senator Obama and convey the news," Foster said. "That should serve as evidence that the sense and intent of the board was clearly in play without question at that time."
Edwards sidestepped the issue at a news conference.
"I think I'm the one they endorsed," he said, chuckling. "It's a very long and very democratic process. ... But at the end of the day, they decided they supported me."
He then repeated his criticism of Clinton from Tuesday night's debate, pointing to her answer about driver's licenses for illegal immigrants.
"In the course of three minutes, I heard Clinton, Senator Clinton, say two different things. When you get a yes-or-no question, you can't say yes and no."