Based on this, it seems like lawyers are not simply permitted to ask jurors about politics. But that's exactly what they want to know about you, as a juror. Based on your politics they know if you'll vote for their client or against him.

The rationale for preemptory challenges is to “allow parties to remove jurors whom they believe, based only on a suspicion, to be biased.”

What a BIG, FAT LIE. Every lawyer uses these things to stack the jury in favor of his side.