TransCanada Corp. opened one of the largest trade appeals ever brought against the U.S., seeking to recoup $15 billion tied to the Obama Administration’s rejection of the Keystone XL oil pipeline…Obama said the line would have undercut U.S. global leadership on climate change…TransCanada has a “very strong case”…The project’s rejection was a victory for environmental advocates…TransCanada is “wrong to try to force American taxpayers to pay for its mistakes,”…“These lawsuits are about a foreign company trying to undercut safeguards that protect the American people.”  Keystone’s boosters are praising the company for the appeal.  Backers said Keystone XL would create thousands of jobs, increase U.S. energy security, and help an important ally in Canada develop its energy resources…TransCanada has a legitimate argument that Obama ruled on Keystone XL based on political considerations, not on the pipeline itself or the merits of the project…While a tribunal couldn’t force approval of Keystone, it could award damages for costs and lost profit…The TPP includes a similar investor-state dispute resolution system and opponents are using TransCanada’s case to illustrate…how companies can take advantage of the process…