I just don't see how this is retaliation. Moody's is a public company. While the US government could conceivably put pressure on the firm to do something like this, they have a lot more tools at their disposal. In addition, the government has a lot of incentive to keep Chinese capital markets happy. If things go awry, it could hurt the American government even more. What if the Chinese banks decide not to hold any more US debt? It starts a bad cycle. Nobody wins in a trade war.
Well, that's quite a stretch. I don't see where Snowden fits in. Plus, the rating agencies are already under heavy scrutiny over the housing market crisis.
Retaliation? Does not look like it. What proof is there that this has been a political move?
The rationale is justified. Not everyone is bullish on Hong Kong. They could've been inclined to do this already and this pushed them over but this isn't purely a political play.