The White House confirmed Thursday that Canada has postponed the North American Leaders Summit scheduled for next month but would not say whether tension over the Keystone XL oil pipeline is the reason. Canada, this year’s summit host, announced Thursday that the summit will be held later in 2015, though no exact date has been set. Some Canadian media outlets, such as the Toronto Sun, reported that the meeting was rescheduled because of President Obama’s continued indecision on Keystone, which...