No , he cant.
https://en.wikipedia.org/wiki/Logan_Act
This law was introduced in 1799.
§ 953. Private correspondence with foreign governments.
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, with intent to influence the measures or conduct of any foreign government or of 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.
This section shall not abridge the right of a citizen to apply himself, or his agent, to any foreign government, or the agents thereof, for redress of any injury which he may have sustained from such government or any of its agents or subjects.
1 Stat. 613, January 30, 1799, codified at
18 U.S.C. § 953 (2004)
It is simple . He broke the law, and there is a possibility that Trump is linked to this . If this was Hillary , you would be screaming Treason . But its your boyman and you will just let it slide.