@Nonya_Bidniss
1. Redundancy: The United States already has an interceptor system called Ground-Based Midcourse Defence.
2. Engineering hurdle: Israeli Iron Dome takes out short range rockets not ICBMs. ICMBs travel up to Mach 23 at their peak which gives a max 5 minutes window during take off to intercept. This detection requires hundreds if not thousands of satellites (Brilliant Pebbles) to stay over an adversary country to try and detect small fires during launch.
3.Money: Trump attempted a similar plan in his first term but was rejected because of cost.
4. **MOST IMPORTANT!**: Trump likely thinks this is a literal iron dome.