Like the Dixie Chicks, country-music artists who sparked controversy last year after their lead singer said she was ashamed that Bush is from her home state of Texas.
But for others, it's been a big step to join the anti-Bush campaign.
Bruce Springsteen has been reluctant to lend his name or music to past election campaigns, but told the music magazine "Rolling Stone" that he felt compelled to participate this year after the U.S.-led invasion of Iraq: "I felt we had been misled" into the reasons for going to war, he said.
There is a song called "Bushleaguer" by the rock act Pearl Jam. Its leader singer, Eddie Vedder, has been a strong critic of the Iraq war and the Bush White House. The song contains the lyrics: "A confidence man, but why so beleaguered? He's not a leader."
The "Vote for Change" tour will take in nine so-called "battleground" states where the presidential race is tightest.
The musicians want to encourage voters who are undecided -- or who are considering staying at home -- to go to the polls.
The campaign to re-elect Bush has no equivalent tour. But that's not to say the president has no fans among popular musicians.
Several performed at the Republican Party Convention in New York last month. Among them was Christian singer Michael W. Smith. The Republicans also enjoy strong support among popular country music acts, like Brooks & Dunn. So both parties are using music to get their political message out.
There's nothing new in that -- politics and music have a long history together. And artists around the world have often put their feelings about major events -- most recently the Iraq war -- to music.
But this year has seen popular musicians become more politically involved than in any recent election. John Carey is a spokesman for America Coming Together, a Democratic activist group that will use the proceeds from the "Vote for Change" tour to try to influence voters in the battleground states: "It is unprecedented to have a lot of these rock stars -- who might sometimes be hesitant about coming out against the Bush administration -- [go on tour together]. The stakes are high, people are very energized about this election, because of the impact our election is going to have throughout the world."