At the risk of repeating myself...
US Title 52
§30121. Contributions and donations by foreign nationals
(a) Prohibition
It shall be unlawful for-
(1) a foreign national, directly or indirectly, to make-
(A) a contribution or donation of money or other thing of value, or to make an express or implied promise to make a contribution or donation, in connection with a Federal, State, or local election;
(B) a contribution or donation to a committee of a political party; or
(C) an expenditure, independent expenditure, or disbursement for an electioneering communication (within the meaning of section 30104(f)(3) of this title); or
(2) a person to solicit, accept, or receive a contribution or donation described in subparagraph (A) or (B) of paragraph (1) from a foreign national

Veselnitskaya is a Russian National.  Trump Jr. accepted a meeting offering "dirt" on Hillary, "a thing of value".  Illegal per this section.