Also I think think Jellico exploited Data. Data doesn't lie unless the situation calls for it. And Jellico needed a "yes man" as his XO. Riker couldn't fit that role, especially since he was out of the loop.
Data was not a "yes man". He carried out orders that were possible and when the orders could not be carried out he said so and explained why. It's to Jellico's credit that despite the enormous pressure he was under, he was able to swallow his pride and subdue his command ego and back off to a doable stance.