It would be the hight of stupidity on their part to do this.
A trial would simply illustrate the stupidity of their own position on thigs like interrogations, etc, while turning Bush’s image from that of a very unpopular President to a martyr.
But then they are Democrats and hence not very analytical - even dumber at times than Republicans and that says a lot.
The left will need something for misdirection from the problems they will inevitably incur from day one.
A new terror attack on America or Americans? Look at the Bush criminal conspiracy.
Iran won't play nice and lies to O? Bush war crimes alienated Islam.
The economy continues its collapse? Look at how alienated foreign economies. (ignoring his adhering to liberal economic policies)