Governments circumvent the tougher WTO rules when imposing much protectionism. Chart available here.
Since the first G20 summiti in November 2008, around 40% of protectionist measures imposed are covered by tougher WTO rules. Therefore, governments have frequently resorted to measures covered by weaker or no WTO rules. It would be wrong to conclude that the WTO rules have had no effect, rather that WTO rules have affected the composition of crisis era protectionism. Given how incomplete the set of WTO rules are--and therefore that circumvention remains possible--such evidence makes it hard to argue that the WTO rules themselves have limited protectionism. The source of any restraint probably lies elsewhere, at the national level.