If you talk to anyone who has worked in U.S. intelligence you'll find out that Israel today is no more trustworthy than the Soviet Union was at the height of the Cold War. So anyone who thinks this Pollard guy should be pardoned by the U.S. -- and by a Republican president, no less -- is either naive or stoned.
This has always been the case. No one trusts the other, absolutely. Even the British have limits to how far the alliance can be stretched to.
And this is a good thing. Don't forget, Israel is no posterboy of morality; that country has sold sensitive American technology to China, including plans for the co-developed Lavi fighter plane, and almost sold the Phalcon AWACS. I can't exactly blame Israel; they were looking after their interests.
In realpolitik, trust is of poor value, no matter how much jingoism is added to the mix. Overall, parallel interests matter more, and this in itself is enough for Israel and America to value each other's common interests.