"Europa isn't Mars, and studying and eventually getting humans to Mars is NASA's current overriding goal. Pure politics. Several of the Congressional leaders who are strongly backing the Europa mission and planetary exploration in general are highly conservative politically. While they favor spending more money on planetary missions, they also want to cut funding for missions for NASA to study the Earth, especially climate change. Essentially proposing to push out the launch of a Europa mission to forever may be part of a hardball negotiating tactic to trade more funding for the Europa mission for also fully funding the President's generous proposed budget for Earth science missions."
Keith's note: This is hilarious. The Planetary Society is using the "politics" dog whistle when in fact politics is all that they engage in when they lobby Congress for their referred projects - and against those they do not like. In this case, they are not getting their way, so, of course it is due to that horrible Washington scourge called "politics". What will be fun to watch is when the Planetary Society eventually realizes that the only way that they are going to get their preferred Europa mission ala Rep. Culberson, is to fly it on a SLS. That means that they will have to start lobbying for SLS - and against (or not in support of) Earth science and/or commercial crew (where their extra Europa money will come from). Of course SLS is at the heart of NASA's #JourneyToMars so the Planetary Society will have to start to support that effort (which is also eating Europa funds) and not their Almost-Mission to Mars concept.