Quotes from the news wire:
There was a political imperative on the government to get an agreement and then to go to the electorate with the claim that they had, to coin a phrase, got Brexit done, i think it possibly was the case in some senses that it was `make the agreement in haste and then repent at leisure. And what were seeing now is the repentance.
Cameron has painted himself into a corner when it comes to in-work benefits for EU migrants: it was a bone he threw to his skeptics without thinking it through, but having promised it, he's going to have to deliver something. The problem is whatever he gets now could end up looking worse than nothing at all.