Philippine President Rodrigo Duterte has threatened to jail critics if they try to impeach him, as he faces accusations of defending Beijing after a boat crash in the disputed South China Sea.Duterte enjoys firm popular backing but his setting aside of the standoff with China over the resource-rich waterway is criticised as weakness by some in the Philippines.The issue has flared up since a Chinese fishing trawler hit and sank a Filipino boat on 9 June near Reed Bank, an area that is within M