Since Senate Majority Leader Mitch McConnell (R-KY) refused in 2016 to allow a vote on President Obama's pick, Merrick Garland, to replace the late Antonin Scalia until after the election Democrats are demanding now that he follow the same course this time and hold a vote on Trump's selection until after the November midterms. Their hope is that the Democrats will be able to retake the Senate in November and thus block any conservative Justice that Trump would nominate.
It's not clear that the Democrats have much of a chance of regaining power in the Senate, but that aside, their demand that McConnell treat this nominee as he treated Judge Garland on pain of being guilty of gross hypocrisy suffers from historical amnesia.
Joseph Wulfsohn at The Federalist gives the background:
It was in 2013 when then-Senate Majority Leader Harry Reid (D-NV) established the infamous “nuclear option,” which allows a simple majority in the Senate to approve all judicial nominees with the exception of Supreme Court appointees. At the time, then-Senate Minority Leader Mitch McConnell (R-KY) actually warned his Democratic colleagues, saying “You’ll regret this, and you may regret this a lot sooner than you think.” Well, Reid and the vast majority of Senate Democrats passed the nuclear option in a 52-48 vote.Then, in February of 2016 Justice Scalia died. President Obama chose Garland to fill his seat. Garland would probably have been confirmed if his nomination came to a vote but McConnell cited a suggestion by then Senator Joe Biden, who was now Obama's Vice-President, that the Senate not approve Supreme Court nominees during a presidential election year and allow voters to decide in November whether they want the president's nominee on the Court.
The "nuclear option" allowed judges to be approved on a simple majority in the Senate rather than needing 60 votes. Senator Reid imposed this rule because Democrats had a majority but they lacked enough votes to override any Republican reservations about a particular candidate. By requiring only a simple majority the Democrats were able to ignore Republican concerns about a nominee and fill the courts with liberal judges.
Biden had made this recommendation in order to stall a Republican Court nominee, but the "Biden Rule", as it came to be called, only pertained to nominees in a presidential election year, not a midterm election year. Thus, it seems a little disingenuous for Democrats to demand that McConnell, having invoked the "Biden Rule" to stop an Obama appointee in a presidential election season, do the same now in a midterm year.
Anyway, Democrats were angry about the delay of the Garland nomination, but everyone expected that Hillary would be elected president in November and that Obama's pick would then be confirmed.
It didn't work out that way, of course. Trump was elected, largely because voters were fearful of the havoc a liberal Supreme Court might wreak upon the nation. Trump picked Neil Gorsuch to fill the vacancy, a pick which embittered the left and animated them to do everything they could to prevent Gorsuch from being seated.
They could indeed block Gorsuch because the "nuclear option" only applied to lower court judges, not SCOTUS appointees. If the Republicans couldn't get 60 votes to confirm Gorsuch his nomination was dead. McConnell warned his Democrat colleagues that if they continued to obstruct Gorsuch's nomination he’d be willing to change the Senate rule to require only a simple majority for SCOTUS nominees as well as other judges. The Democrats didn’t yield, so McConnell had the rule changed and Gorsuch was ultimately confirmed.
Here's Wulfsohn again:
[The] Democrats are trying to use McConnell’s 2016 political maneuvering against him, saying that the Senate should halt the nomination process until after the election. But even the Washington Post had to call out their BS since McConnell [following Biden] stressed the Senate shouldn’t approve nominees during a presidential election and not during midterm elections.In other words, the Democrats are reaping what they themselves have sown. They were warned that this would happen, but they put political expediency over political prudence and now McConnell is making them pay.
Plus, Sen. Minority Leader Chuck Schumer (D-NY) and Sen. Dianne Feinstein (D-CA) have conveniently forgotten that the Senate confirmed President Obama’s SCOTUS nominee Elena Kagan in August 2010, just months before those midterms.
So, President Trump will name a nominee within the next few weeks, and barring some sort of revolt against Trump by squishy (Collins, Murkowski) or spiteful (McCain, Flake, Corker) GOP senators, that nominee will be confirmed.
The Court will then, probably, have five Justices who believe that the country should be run in accord with the Constitution and not current political fashion.
It could make a substantial difference because even though Kennedy often sided with the Court's conservatives there were key cases in which he did not.
But the really troubling news for the left is that it's quite possible that the Republicans will hold power in the Senate in November and that Trump will get to appoint at least one more Justice before 2020. We'll see. Meanwhile, the left being what it is, the next couple of months could get very ugly.