Key decision in XL size but is it set in stone?

Conservative opponents consoled themselves after Barack Obama's re-election in 2012 that he was now a lame-duck president and for two years, that appeared the case, but with the 2014 Congressional elections and a Republican-dominated Congress, Obama seems to think that the shackles are off and he can act on his own terms.  There was the nuclear deal with Iran, which was the only logical outcome.  Also, Obama has openly talked about racism in America and other controversial subjects.  There was the re-establishment of diplomatic relations with Cuba.  Significant penal reform is in progress.  Importantly, he has had the Environmental Protection Agency institute stringent measures on emission.  Many of his decisions have had to come via Executive Order allowing Republicans to paint him not being bipartisan when after a half a dozen years, Obama has realised they don't believe in compromise, with him or any other Democrat - it's either surrender to Republicans demands or we'll paint you in the media as being partisan.  There are still many Democrats who perform the kowtow.
As with the EPA, Obama has taken an environmental decision but had to dress it up commercially, when it came to finally rejecting the Keystone XL pipeline.  XL may have become a common size in America but like occupants of such clothes it was was far from healthy.  The project would have transported ultra-dirty tar sands oil in a pipe crossing some of the most pristine landscapes in the USA (so there would be damage during construction and with any possible leakage thereafter) and would have created next to no jobs once it was completed.  It's no surprise that this has come shortly after the landslide victory of the Liberals in Canada, who did support it but not as vocally as the 'evil Dubaya' of Stephen Harper.  Therefore the diplomatic repercussions of permanently refusing to allow it to be built, from the tar sands fields of Canada to the Lousiana coastline, are reduced.  Until the Liberals came to power, Obama kept postponing the decision so as not to offend Ottawa.
The Republican presidential hopefuls seemed to have learned nothing from 2008 and 2012, with their sole policy platform being to repeal everything Obama has done in the last two years, plus unravel the entrenched Obamacare, which has overcome its teething issues and legal challenges.  Such vitriolic negativity is hardly, the 'Good Morning, America' of Ronald Reagan but maybe that's not surprising given the quality of candidate, need for the oxygen of publicity and fear of failure.
Donald Trump is a walking parody, Carly Fiorina is not mealy-mouthed but still gauche (a female Mitt Romney) and Ben Carson is a neurosurgeon who seems to have transplanted his own brain.  These are the three front-runners and all are non-politicians (Fiorina's bid for the Senate crashed and burned).  Carson is outstripping Trump as the most quotable, for all the wrong reasons, Dan Quayle-style.  He has linked gun control to the Holocaust (a sure sign of a rogue if they have to use this tactic to make political capital), says a Muslim should never be US president and has restated the belief of his that the Biblical Joseph built the pyramids as grain stores, not pharaonic tombs (though most pyramids were built 1,500 years before Joseph would have been in Egypt).  Now, Sid Meier's Civilization II is a landmark in PC gaming and enjoyable as it is, it's not strictly historical (building the Eiffel Tower improves your diplomatic reputation, building the Great Wall gives each of your cities a wall), so when list the pyramids as putting a granary in each of your cities, they are using some artistic licence.  In the original Sid Meier's Civilization construction of the pyramids gave you the choice to select any governmental form - goodness know what Carson would have made of that.
The other hopefuls (never was a word more appropriate) are career politicians: Jeb Bush (or Jeb!) is sinking without trace, as is Chris Christie (every immigrant should be treated like a Fed Ex parcel).  Scott Carson (build a wall on the border with Canada, to limit immigration and terrorists...) has gone already.  Marco Rubio is still in with a real good shot though and is the most dangerous to any Democrat candidate.  Hillary Clinton may not be perfect but she's better than all the Republicans put together and unlike all of them, she won't reopen the XL pipeline project.