Bojidar Marinov says:

In the 1890s, the Roman Catholic bishop of New York complained that the Roman church is losing a large number of its members among the coming immigrants. And that almost immediately after they leave Ellis Island.

The reason?

The Presbyterian churches of New York had an round-the-clock watch to wait for the groups of immigrants who came out of the immigration facility on Ellis Island, and offered them temporary shelter and English courses, as well as low-pay temporary employment in the city. (While politics was controlled by the Irish mafia of Tammany Hall, the business in the city was controlled by Presbyterians and Dutch Reformed. It wasn’t until John D. Rockefeller – a fundamentalist Baptist – moved his Standard Oil headquarters to NYC that a major non-Presbyterian player appeared on the market.) This changed the play field entirely.

Keep in mind that 65% of the Arabs in the US are Christians. At least half of them have converted AFTER they arrived. Of those who don’t convert, the vast majority either become secularized, or have already been secularized in their home countries.  There is no reason why the [current crop of refugees from Syria] won’t have an even higher percentage of conversions.