Just curious but if SCOTUS is not the arbiter of the constitutionality of legislation, who is ?
Originally it was intended to be the Congress, and the States. SCOTUS was to be the weakest branch of government, and not the legislative branch as it has become. Just as the Constitution limits the power of the Federal Government, the judicial power of the Supreme Court was limited in Article 3, section 2.
James Madison:
“The States then being the parties to the constitutional compact, and in their sovereign capacity, it follows of necessity, that there can be no tribunal above their authority, to decide in the last resort, whether the compact made by them be violated; and consequently that as the parties to it, they must themselves decide in the last resort, such questions as may be of sufficient magnitude to require their interposition.”
In further regards to the selection of justices, and the failure of McConnell to act, they are relying on what is called the "Biden Rule" from a speech given by Joe Biden while Senator in 1992. Here is what McConnell said in 2001, and 2005:
http://thinkprogress.org/justice/2016/02/19/3751232/mcconell-grassley-scalia-debunked-by-mcconnell/
"Back in 2001, shortly after George W. Bush’s controversial inauguration, however, McConnell argued that the Republican president should be given a free hand to shape the courts. At a June 26 Judiciary Committee hearing, McConnell noted his long support for this principle. “My view then and my view now is that the President won the election, no matter what the margin, and is entitled for the most part to tilt the judiciary in the direction that he feels appropriate.” He added that the “appropriate role of the Senate is largely… to judge the competence and the integrity and the fitness of a judge to be on the bench.”
2. Past Precedent
Another argument the senators make in their recent op-ed is that the Senate has not recently confirmed a nominee this late in a presidential term. “Rarely does a Supreme Court vacancy occur in the final year of a presidential term, and the Senate has not confirmed a nominee to fill a vacancy arising in such circumstances for the better part of a century,” they observe.
But the fact that no justice happened to die in the final year of a president’s administration in recent years does not change the fact that since 1900, six justices have been confirmed during a presidential election year. And just one seat was left open for more than 301 days since the court went to nine justices.
Just 11 years ago, McConnell objected to these sorts of procedural delays. In a July 20, 2005 floor speech in support of the John Roberts nomination, he said:
Slow walking the process beyond historical norms and engaging in a paper chase simply to delay a timely up-or-down vote are not hallmarks of a fair process. The Supreme Court begins its new term on October 3. As Senator Frist has pointed out, the average time for a nomination to confirmation for the current justices was 62 days. The average time from nomination to confirmation for President Clinton was 58 days. Justice Ginsburg was confirmed in only 42 days. The Senate has 72 days to complete action on Judge Roberts’ nomination, in time for him to join the Court by the start of its new term, October 3. By any standard, that is a fair goal. What is not fair and what is, quite frankly, a little curious is for some of our colleagues who, before even having heard a single word of testimony, have already come up with excuses as to why we should depart from this historical standard. It is disturbing that they seek to justify so far in advance why the Court should begin its proceedings at less than full strength."