Actually, the US said the oil would be produced regardless of Keystone going ahead or otherwise so nixing it would have no impact on CO2 emissions.

But you're missing the point - Harper has no diplomatic skills and a track record of failure in US/Canada relations- he's not a serious source of advice.

Obama's a politician with a constituency- just like Harper.  Only one of those constituencies was happy with the political outcome of Keystone.  Harper was so peeved he cancelled the 3 Amigos Summit - not a diplomatic bone in his body.