Just this once, OK? That sums up Prime Minister Stephen Harper’s terrified assent to China’s $15-billion CNOCC takeover of Calgary-based petroleum producer Nexen. From now on, he promises, he’ll only say yes under “exceptional” circumstances. Harper had offered himself up to NDP Leader Thomas Mulcair on a platter, and Mulcair set the platter on fire during question period. It was fun to watch but that’s little comfort. Nexen’s an awful deal for Canadians.