You have to remember that 1916 had not only World War I in full swing, but the Easter Rising had occurred in April of that year and many Irish Americans were pissed at Wilson for his Anglophile foreign policy. Irish Independence leaders in the US went as far as to throw their weight behind Charles Evans Hughes, a Republican (the horror), because he was at least "an honorable man".
It's quite funny that when De Valera arrived to the United States, he was confident Wilson will receive and recognize him as "President of the Irish Republic".
On a side note, Wilson was accustomed with using term "unAmerican" well before his political career, in his academic writings, though, arguably, it wasn't that uncommon at the time.
