For starters, I think that the way the Senate handles this will determine who the nominee is for President by the Republicans. Should the Senate stand firm and not conduct hearings on Obama's nominee for the Court, some faith will be restored to the Republican establishment by the Republican conservative base and there will be far less enthusiasm for supporting Trump. But should O'Connell start to give in to media and Presidential pressure, or should enough Republican Senators shift to supporting Obama (rationalizing that a President gets to pick his own nominees and that the Senate should only be looking at technical competence to do the job), the outrage in the Republican base will make the current situation seem like nothing, and without a doubt voters will turn to a "strong man" to lead the nation, i.e. Donald Trump.
All of the above assumes that the Court will not go into recess and thus not give Obama the opportunity to make a recess appointment, or it could go into recess and not convene until after a new President is in office, who could then withdraw the previous President's temporary appointment.
While appointment of a liberal or centrist Justice would be certainly harmful to the goal of having a court adhere to the Constitution, it would likely be disastrous for the 2nd Amendment. Both the Heller and the McDonald decisions were decided on a 5-4 vote. With a changed court that accepted any 2nd Amendment related case we could find a full repudiation of the 2nd Amendment as an individual right, giving a green light to every and all gun control law proposed in the leftist controlled states and cities. It would be terrible, but interesting, to see how the American public would react to a major loss of 2nd Amendment rights, now with almost 15 million people (my estimate) concealed or open carry users who have been accustomed to using their gun rights on a routine basis. Millions and millions of new guns have been added to the hands of the public since Obama has been in office, and I doubt that gun owners will all meekly submit to new restrictions or laws ordering gun confiscations. I have long felt that even today we are really two countries, one that holds to the 2nd Amendment, and one that despite the Supreme Court rulings has shown total disdain for the right of ordinary citizens to "keep and bear arms". States like NY, NJ, MA, MD, CA, HI and possible a few more would be free to pass and seek to enforce draconian anti-gun laws while strong Republican led states would likely react with even more gun rights supportive legislation. This would set us up for more than courtroom battles between the Red and the Blue states.
Until we see when and if Obama makes a nomination, and then how the Senate handles it, all of this is just speculation. I am hoping that with a delay in replacing Scalia until the White House is occupied by a Republican, combined with one or more retirements of liberal justices during the next Administration, that we will see a court move strongly, with a 6-3 or even 7-2 majority reaffirming and strengthening the 2nd Amendment as a basic American right.
