I'll let you do your own research, but here, try these....
Anarchist Musicians
The Musician's Role In Politics
Making Marx In The Music
Music And Politics
On a more personal note: Music and politics have competed for, shared, and controlled people's understanding of the world around them. In the early times word of mouth was the number one source for information, and it primarily came in poetic legends and bardic songs. There have been times when music turned anti-governemnt, anti-war and so on. But there have been times when (subliminally) more empathical political views have been expressed through music. A musicians positive political views are often the basis for certain songs. Just as like, some politicians will reference the music of the time for research or quotations. Music provides valuable insight into public opinions, thus it is a valued asset for a politician to have an understanding of modern music. Just as it is important for musicians to have a similar understanding of modern politics. Both are always on the public's minds, so both have equal (even if differencial) effect on each other.