I would NEVER vote for someone just because a star, rock or otherwise, endorsed them, but some popular music can be fairly political. Just listen to a sampling of the music that was popular on the airwaves in the 60's during Vietnam. That was some pretty powerful stuff.

And a fair amount of 80's punk rock was a political barometer of sorts, the Dead Kennedys being the most obvious example. Lately, NOFX are trying to be the musical antagonist to Bush II that the DKs were to his father. Frank Zappa skewered politics and politicians regularly, particularly in the aborted '88 tour (which generated three albums full of potshots at pompous politicians, the religious right and Jimmy Swaggart).