As migration flows increase, native populations often respond with calls for more restrictions on naturalization. It is easy to imagine the reasons for this. Given that citizenship and naturalization offer access to political participation, and also provide full access to the local welfare state, native populations may often conclude that rising numbers of new citizens from various “outgroups” could be a politically destabilizing factor. Other natives may fear that large numbers of new migrants place fiscal strain on public benefits.
This illustrates the interplay between immigration policies and naturalization policies. Strictly speaking, immigration and naturalization are separate phenomena, but in practice, high levels of immigration tend to lead to calls for restricting new migrants’ access to citizenship. The reverse is often true as well.
In a 2010 empirical study on the determinants of new restrictions on naturalization, Graziella Bertocchi and Chiara Strozzi conclude that high migration levels impel local policymakers to introduce new restrictions on jus soli:
our results suggest that migration moves national legislation in the direction of jus sanguinis, not jus soli. In particular, when we take into account the legal tradition governing citizenship, we find that countries with a jus soli origin react to increasing migration by adding jus sanguinis elements. …
Our investigation reveals that migration has an overall negative effect on liberalization of citizenship legislation and adoption of jus soli elements. Moreover, a country’s legal tradition affects the way that it responds to migration. In particular, jus soli countries react to increasing migration through restriction.2
The dwindling birthright citizenship countries is due to the ability of immigrants to come in and take up the social support that the natives have paid for without adding to the economy or the social net. In other words, they come for the freebies and the locals don’t like it. This is why Trump is going to make sure that birth tourism will be a thing of the past or he will restrict immigration so as not to include the families of “birthright” foreign tourists.