Be sure to check out Elizabeth Nolan Brown’s summary in Reason of some recent research on collective outrage:

Ultimately, the results of Rothschild and Keefer’s five studies were “consistent with recent research showing that outgroup-directed moral outrage can be elicited in response to perceived threats to the ingroup’s moral status,” write the authors. The findings also suggest that “outrage driven by moral identity concerns serves to compensate for the threat of personal or collective immorality” and the cognitive dissonance that it might elicit, and expose a “link between guilt and self-serving expressions of outrage that reflect a kind of ‘moral hypocrisy,’ or at least a non-moral form of anger with a moral facade.”

Here are the key findings, quoting from Brown:

1. Triggering feelings of personal culpability for a problem increases moral outrage at a third-party target.  …
2. The more guilt over one’s own potential complicity, the more desire “to punish a third-party through increased moral outrage at that target.” …
3. Having the opportunity to express outrage at a third-party decreased guilt in people threatened through “ingroup immorality.” …
4. “The opportunity to express moral outrage at corporate harm-doers” inflated participants perception of personal morality. …
5. Guilt-induced moral outrage was lessened when people could assert their goodness through alternative means, “even in an unrelated context.” …

Of course, these days, all social science comes with a caveat about replication, but this particular study sure does feel familiar and explanatory of behavior we can observe every day in the political field.