For the American readers: Imagine a political candidate's radio or TV commercial. They usually go like this "[so-and-so] cares about [thing-and-such]. [yadda-yadda], Your right to [thingers] means [blah]. I'm [so-and-so] and I approve this message.". Replace the candidate's name with a political party and you get a sense for what the advertisements are like. Are they "propaganda" or simply "getting the word out" for a political cause? I'm not sure myself....
I agree with ilaksh - it is a "little weird" to be in the U.S., listening to main-stream U.S. music, and to have the only interruption be some political message about Mexico.
If anyone is interested, I can record some and post them -- not to push any agenda one way or the other; just to share.
Edit: Here's a youtube video that I found. This video sounds like a montage of commercials. It's representative of what you'd hear between songs in one single go.