I'm quite confident that we can take out any long range missile that is headed in our general direction AND manages to get out of the atmosphere. I don't think we have a reliable boost-phase antimissile capability.
The geometry doesn't let us intercept missiles on the way up. Missiles on the way down that land far away from the defense missile launch site.
For example, missile sites in Alaska and California don't help much against missiles launched at Pago Pago.