The immigration reform bill headed to the Senate floor lacks the 60 votes it needs to advance and will likely have to be partially rewritten to win congressional approval, proponents of the bill said.

Democratic and Republican sources working to build support for the bill agreed that garnering the necessary GOP votes would require amending the legislation to strengthen its border security components. Additionally, there are senators on both sides of the aisle who don’t support the current measure because of provisions other than border security who also must be appeased.