The Mode of Electing the President
Nothing was to be more desired that that every practicable obstacle should be opposed to cabal, intrigue, and corruption. These most deadly adversaries of republican government might naturally have been expected to make their approaches from more than one quarter, but chiefly from the desire in foreign powers to gain an improper ascendant in our councils. How could they better gratify this than by raising a creature of their own to the chief magistracy of the Union? But the convention have guarded against all danger of this sort with the most provident and judicious attention. – Alexander Hamilton, Federalist No. 68
While Hamilton is speaking here specifically of assurance that the members of the Electoral College themselves might not "be tampered with beforehand to prostitute their votes," it seems pretty clear that the underlying concern is foreign meddling in presidential elections. Just saying.