The idea that shrinking population might be the reason for the push to Islam in America by many in power (who is behind it?) is inconsistent with the evidence that birth rates are above replacement levels in the US (israel, too). Religiosity is also surging in both.
So, now what could be the motive other than taking down the US? Perhaps taking down the US level of consumption (use of raw materials) as I postulated earlier before population came to mind?