I expect you're right that no crime was committed by Junior.  But boy, was it close.

The US Bipartisan Campaign Reform Act of 2002 prohibits foreign nationals from making expenditures to expressly advocate the election or defeat of a political candidate.

Under the US Federal Code "Whoever, knowing that an offense against the United States has been committed, receives, relieves, comforts or assists the offender in order to hinder or prevent his apprehension, trial or punishment, is an accessory after the fact."

Junior coughed up his emails precisely because failing to do so would have been a crime.