Bahrain smashed their Shia rebellions during arab spring with tanks, but that was blessed by USA as opposed to the attempted smashing by Syria and Lybia of their own rebellions.
With Saudi Arabian provided mercenary tanks (because Bahrain's own army is at least partly Shi'a), and this was definitely not "blessed" by the USA. Tolerated, maybe, in the sense that the US was not going to create a shooting war with Saudi Arabia to stop this, yes.
Don't oversimplify it. The USA is constantly pressuring Bahrain into allowing the Shi'a a voice in government, and every 6 months or so, Bahrain expels yet another American diplomat for mentioning the Shi'a.
