The extra money would be for financing the Iron Dome missile defense system against rocket attacks on Israel The U.S. has already spent 205 million for the system. Now the Republicans are pressing to pass a bill that would add another 680 million.
This year alone the Obama budget pledges 3.1 billion in funds towards Israeli security. This is part of a 30 billion ten year U.S. pledge The Iron Dome funding is on top of this!
Israel itself had decided to defund the Iron Dome system. The missiles used to knock down the incoming missiles are far more expensive than the incoming missiles and the system is not cost-effective it was decided. However, now the U.S. is footing the bill Israel is pressing to expand the system. The system is not designed as protection against long range missiles such as Iran might use.
The Pentagon is a cheer leader for the system praising its effectiveness during recent attacks..Yet some Israeli officials were critical of the performance which is why they claim much more is needed. Although quite cheap most of the rockets coming from Gaza are practically useless but once in a while they do cause some damage or deaths.
Obviously the deficit is not a big issue for the Republicans when it comes to funding Israeli military projects. We will see what the Democratic response will be in this election year. For more see this article.