It is my understanding that the child could be claimed as a Qualifying Relative because they are a US Citizen (hold a passport), and therefore can be treated as a resident for tax purposes.
As far as I can tell, you would not be able to claim the Child Tax Credit because you do not meet the residence test (the child must live you with for more than half the year), and therefore do not meet the requirements for a Qualifying Child for the CTC.
But as of 2018, you would be allowed to claim the $500 Family Tax Credit, under the 2017 TCJA, by claiming the child as Qualifying Relative.
I'll keep looking into these rules, but this is what I've concluded thus far.
