Sympathy for the favorite nation, facilitating the illusion of an imaginary common interest, in cases where no real common interest exists, and infusing into one the enmities of the other, betrays the former into a participation in the quarrels and wars of the latter, without adequate inducement or justification. It leads also to concessions to the favorite nation, of privileges denied to others, which is apt doubly to injure the nation making the concessions; by unnecessarily parting with what ought to have been retained; and by exciting jealousy, ill- will, and a disposition to retaliate, in the parties from whom equal privileges are withheld. And it gives to ambitious, corrupted, or deluded citizens, (who devote themselves to the favorite nation,) facility to betray or sacrifice the interests of their own country, without odium, sometimes even with popularity; gilding, with the appearance of a virtuous sense of obligation, a commendable deference for public opinion, or a laudable zeal for public good, the base or foolish compliances of ambition, corruption, or infatuation. I think Washington is talking about the dangers of having possible patriotic ties to another nation via family. With an American President this could lead to a significant conflict of interest on the needs of America in conjunction with the individuals needs to help the other country
This is what we have now with Obama, whose father being born in Kenya whisked baby Obama away and had him grow up in Kenya and Indonesia and is now the President of the United States, Obama the man has too many conflicts of interest to ever put the interests of the United States first. We elected the very thing our forefathers were scared could happen.