Take trump name out of it. X has russian spy material that is so ultra sensitive that it should not be handed to Y running for office and Z is notified of that fact. Its so spy like that It must go though cutouts with Z being told he will have to make decision on whether to show to Y.
When does it become illegal. Hand off?? Use???.depends on mAterial? ??? Or never?
Receipt of the material isn’t illegal - unless the material itself is classified by the US Government. And even then, turning it in should take care of the issue.
If the intent in receiving the material is to commit a crime (such as blackmail), or if one *knows* that the information was illegally obtained, then seeking and receiving the info is likely illegal.
However - it is important to remember that opposition research is completely legal, even when done from sources outside the country. Use of false info (like the golden showers dossier) can be defamatory, but that bar is set pretty high in public life.
I am not a lawyer, but the above makes sense to me.