Here is the best post I've seen so far on why this bill allowing the Iraqi parliament to grant amnesty to Iraqi insurgents, even ones that have killed American soldiers, was actually supported by the Republicans and voted for by no fewer than 19 Republican senators (no Dems voted for it). Digby has found some very poignant links; I suggest you check them out.
Yet I confess, I don't get it. Seriously, I can't wrap my head around this issue. Why on earth did the Republicans support such an abomination? No amnesty for people coming to America in search of a better life, but amnesty galore for those who plant roadside bombs and shoot from the shadows at American troops? WTF?