According to Sen. Lindsey Graham (R-S.C.), the bill will "basically say in law for the first time that the homeland is part of the battlefield" and that someone suspected of ties to Al Qaeda can be locked up without trial whether he is an "American citizen or not."

Its odd that Congress would choose this moment to formally extend the "battlefield" to the domestic United States, allowing for military detention of US Citizens on US Soil. The legality of Jose Padilla's military detention was never fully adjudicated, and herein Congress would bless it. This is really the end of the road for habeas rights in the US. Obama is fortunately threatening to veto this - it may be the moment when he finally differentiates himself from the Bush administration on civil liberties.

My question is why right now? Why didn't they do this years ago if they wanted to?

I suspect this might be political cover for something else in this bill - one way to kill a bill you oppose is to vote against it - but if you can't, you can make it so radical that the other side won't support it any more.

Is the President's Indefinite Detention Power Limited to Foreigners? - Hit & Run : Reason Magazine