"It is telling that the United States has always been more concerned with the disclosure of those documents than with the damning substance of the disclosures."
But note that "the United States" here not only refers to the government of said country, but to its citizens too. Nobody is up in arms about it. It made the news, it died off, that was it. Nobody cares (generally speaking, of course there are people who care).
That's why they can continue, because nobody's really surprised, shocked, or even disappointed... the average American or indeed their allies just don't care about that.
That's my problem with all the Wikileaks stuff - they claim it's ground-breaking, world-changing, risk-your-life-for stuff and - actually - nobody cared. Was it really worth whistleblowing for the response obtained? And doing so so badly and amateurishly (trusting Assange, for a start, not to mention just chatting about doing it with random people online). Same with Snowden, Assange himself, etc. was it really worth it? All they've done is taught every whistleblower to shut their mouths because hardly anyone will back them, and the full force of the law will descend on them, until they are living under Russian "hospitality", imprisoned after exile inside an embassy, or imprisoned indefinitely.
Not to mention "refusing to testify" is the most ridiculous thing ever (are you listening Mr Trump?). You testify. You note your objection at the start (about whether or not you think it's a kangaroo court) and then you testify everything you're willing to. You co-operate. Because in no other circumstance are you ever going to see daylight.
You're not being asked to lie. You're not being asked to arrest Assange personally. You're not even being asked to drop him in it. You can refuse or deny certain knowledge if you like. That's what people do, even in the full face of the cameras, in such things. But "not testifying" is just going to hurt you and only you, and hurt bad, and for a long time.