OMG how stupid are these people? He just admitted that his son met with representatives of a foreign Government in the hopes of getting information on his opponent. That's Attempted Collusion even if it didn't go anywhere!
Legally, it's probably Conspiracy to commit offense or to defraud United States which can be a felony of up to five years in jail.
It's also likely conspiracy to commit election funding fraud, specifically
Section 319 of the Federal Election Campaign Act of 1971
(2 U.S.C. 441e) is amended—
(1) by striking the heading and inserting the following:
‘‘CONTRIBUTIONS AND DONATIONS BY FOREIGN NATIONALS’’; and
(2) by striking subsection (a) and inserting the following:
‘‘(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 304(f)(3)); 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.’’
and then we have the question of the Logon act which states...
Any citizen of the United States, wherever he may be, who, without authority of the United States, directly or indirectly commences or carries on any correspondence or intercourse with any foreign government or any officer or agent thereof, in relation to any disputes or controversies with the United States, or to defeat the measures of the United States, shall be fined under this title or imprisoned not more than three years, or both.
Which would certainly come into play if, as believed, sanctions on Russia were discussed in return for political information.