The U.S. wants to withdraw its support for development of the Israeli Arrow anti-ballistic missile system. About half the $2 billion cost of developing Arrow has come from the United States. In addition, American firms have done some of the development work, or contributed technology. The U.S. wants to cut the several hundred million dollars it would be spending on future Arrow development, in order to save money, and allocate more resources to U.S. anti-missile systems (Aegis SM-3, THAAD and GBI). American support of Arrow was originally sort of an insurance policy, in case similar U.S. effort didn't work out.
Israel has two batteries of Arrow, and over a hundred missiles available. An Arrow battery has 4-8 launchers, and each launcher carries a six missiles in containers. The Arrow was developed to knock down Scud type missiles fired from Syria, Saudi Arabia or Iraq. The two ton Arrow I is being replaced with the 1.3 ton Arrow II, which can shoot down longer range ballistic missiles fired from Iran. Israel is currently developing and testing an upgraded Arrow II, which can take down longer range Iranian missiles.
The U.S. has provided Israel with a mobile X-band radar that enables it to detect incoming ballistic missiles father away. Currently, the Israeli Green Pine radar can only detect a ballistic missile fired from Iran when the missile warhead is about two minutes from hitting a target in Israel. The X-band radar would allow the Iranian missile to be spotted when it was 5-6 minutes away, enabling the Israeli Arrow anti-missile missile to hit the Iranian warhead farther away and with greater certainty. Israel also wants to buy a land based version of the Aegis anti-missile missile.