Is there evidence to suggest that the US government will not suppress speech that they deem to be a threat to their power? There was rampant blatant suppression

Is there evidence to suggest that the US government will not suppress speech that they deem to be a threat to their power? There was rampant blatant suppression of supposedly communist-friendly speech in the 1950s and 1960s. Does anyone think this has significantly changed? For a more recent example, see how the US government handled the leaking of its diplomatic cables, something which (unlike late night comedy) actually threatens the reputation of the US government.