Why didn't the US government, or an acolyte, slap an injunction or similar on papers like the Guardian, NYT, Der Spiegel etc over Wikileaks' various exposes?

If they hate it so bad, why are they so trigger-happy with pseudo-legal processes rather than pursuing proper remedies? As I understand it the documents lifted were classified; does a means exist of indefinitely preventing publication? In the States? In the UK? Any insight appreciated.