i will be as clear as i can.
these missiles are intended to intercept incoming icbms. they would utterly fail against the icbms that russia has today. utterly. completely. they wouldn't hit a single one.
that means that while the united states still has a serious response capacity, it's a sitting duck. as of right now the united states would be unable to defend itself against a russian or chinese first strike. nor would these missiles have any utility if launched against russia or china.
what can the americans still do with these missiles? they can attack inferior military forces like iran. likewise, the russians can't do much with their own legacy missile stockpile besides use it up somewhere like ukraine.
further, the chinese or russians will eventually move newer defense systems into iran. america's time window to strike is short and closing, and then it had might as well dump them into the sea.
that is why this announcement is more important than concerns about us missile shortages:
there are always conspiracy theories when it comes to modern wars. they have varying levels of truth. some of them have no truth at all. the idea that the united states launched this war against iran to use up surplus, legacy and obsolete weapons is likely largely true, and the idea that this is what the russians are actually up to in ukraine is likely also largely true. this justifies the expenditure to congress. in fact, it necessitates it. but the reality is that this is required, even if nobody at the pentagon is publishing essays or op-eds about it.
expect the americans to continue replacing these legacy missiles with modern missile technology as they get used, and not to replace the missiles being used with similarly aged ones.