"But the administration has so far released only limited information to support that conclusion. "

Lugenpresse.  They have released NO information to support the conclusion.

And that is the fundamental proof that these allegations are false.  

IF they had evidence of Russia tampering with the electoral process in favour of one candidate, Obama has only 14 days left to act on it before that very candidate takes office.  And yet, Obama hasn't acted remotely in a way he should if his accusations were true. IF Russia had actually interfered in the U.S. election, the appropriate response would be:

-publication of the evidence for the citizens to see;

-arrests and charges against anyone implicated;

-immediate halt of diplomatic relations;

-bringing the matter before the UNSC.

This present weaselling pantywaist response, coupled with WikiLeaks denials, no evidence provided, and the evasion by intel agencies when asked to report to Congress and the President-elect is the proof.