Clinton's daughter, Chelsea, and husband, Bill, also visited, while Obama supporter Sen. Edward M. Kennedy of Massachusetts campaigned in two cities in the days before the vote.
Both campaigns hit Maine heavily with radio and TV advertising, and voters' homes were being bombarded with pre-taped messages in support of both candidates.
On Sunday, Massachusetts Gov. Deval Patrick, Rep. Patrick Kennedy of Rhode Island and Sen. John Kerry of Massachusetts, the 2004 Democratic presidential candidate, visited Maine caucuses on Obama's behalf. On Clinton's side, Baldacci, Massachusetts Rep. Jim McGovern and New York Rep. Gregory Meeks campaigned.
The high level of excitement contrasted with earlier expectations that the post-Super Tuesday timing of the caucuses would dampen voter interest.
Democrats on Sunday elected more than 3,500 delegates to the state convention. Based on Sunday's votes, delegates are allocated to each candidate.
A competitive GOP race a week earlier also helped to enliven interest in the Maine Republicans' nonbinding caucuses, which were won by Mitt Romney. He dropped out of the race last week, making it likely that Arizona Sen. John McCain would become the GOP nominee.
Associated Press writer David Sharp in Portland, Maine, and Charles Babington in Virginia, Va., contributed to this report.