One meaning of "overt" is "performed or carried out publicly, unconcealed,
not secret." (OED) Clearly a private letter is not a public statement.
Another meaning of "overt" is "patent, evident, apparent, plain, manifest."
(OED) Clearly the statement "My own views are liberal" is patent, evident,
apparent, plain, manifest. Cf. "She faines. . . Not see the mind whose
words it overt made."
I used the word in the second meaning, as the context should have made
clear. It does not depend on private vs. public.