Not only did Fox unfairly attack Republicans with the ad, but in one state, Fox actually used the ad to endorse a democrat who has voted against stem cell research.

This would seem to be the "smoking gun" for Fox's motives. If this was only about stem cell research, there was no reason for Fox to endorse this democrat. In fact, if both candidates were against stem cell reseach, Fox could have withheld his endorsement.

Instead, however, he cut an ad that inaccurately portrayed a democrat as a supporter of stem cell research.

There's little doubt left: for Fox its about politics and nothing else