Reagan was seriously pro-Israel and started the whole US-supported Israeli military funding. source

Jen Kirby - You mentioned that the United States had a big investment in the Iron Dome. Why is that — what’s the US’s stake in this?

Jean-Loup Samaan - Well, first, historically, the US started cooperating with Israel on air defense in the 1980s. So when missile defense became a significant component of defense investment in the US, Israel was very quickly involved. There’s a history of close ties between both countries in that field. So it would seem, in a sense, natural that a consequence of that is to support something like Iron Dome.

I think it was around the end of Obama’s first term, in 2012, that the US put a stronger emphasis on Iron Dome in terms of budgeting. I believe it was probably not just the politics behind it, but also the strategic assessment that the priority is to protect and to strengthen the defense of Israel vis-à-vis these types of rockets.