A somewhat snarky article by Time magazine's chief political correspondent,
Karen Tumulty just appeared. Take it for what it's worth, but it does make sense of some of the puzzling maneuvering, press statements, and background briefings that went on in the run-up to the visit. It also makes it clear that there was some tension between Carter and the Dean camp concerning how to frame the visit, and why Carter was at pains to deny it constituted an endorsement.
...[I]t seemed as though [Dean] had pulled off yet another master stroke in snagging an invitation to appear in public with Jimmy Carter on the eve of the caucuses. Carter, after all, was the man who had put Iowa on the political map in 1976, when a surprise victory there launched him to the White House. While the former President wouldn't endorse Dean explicitly -- such a move would be unseemly in the midst of a hard-fought primary -- campaign aides put out the word that he would do everything but....
The decision to go to Plains wasn't even a close call, Dean later suggested. "When the former President of the United States asks you to go to church with him on a Sunday before the caucuses, I think you probably take that up...."
The summons from Plains? Carter doesn't remember it quite that way. "I didn't invite him, but I'm glad he came," the former President told reporters shortly before he conducted one of his frequent Sunday School classes at Maranatha Baptist Church. "He called me on the phone and said he'd like to come worship with me. ... He called and asked me if it would be all right." As for the timing, Carter's son Chip later told reporters that the former President had also offered Dean dates in February and March. It was Dean -- not Carter -- who picked the day before the caucuses. Dean may not even be the only Democratic candidate who gets to boast a church date with the former President. Carter said retired General Wesley Clark has also asked for an opportunity to visit him in Plains and worship with him, and that he expects to be able to arrange one...
[T]he subsequent public appearance by the two on the Main Street of Plains -- all eight minutes and 25 seconds of it -- fell well short of even a hint at an endorsement by Carter. He praised Dean for his outspokenness against the Iraq War, which Carter also opposed, and the two of them noted that Dean had gotten his start in politics by working in Carter's 1980 campaign in Vermont. What neither one noted, however, was that this was the race that Carter lost.