Here's a list
of possible judges who appear to be well-qualified to be nominated to the Supreme Court. They run the gamut from liberal to centrist to conservative, thus it's possible for Obama to put someone forth that there's no good reason not to approve them. Which would put incredible strain on the Republicans running the Senate to justify leaving a position on the Supreme Court open for an extended period of time. There has been bluster about 'there's never been a justice appointed during an election year!' which is completely bogus, it happened about 30 years ago during Reagan's reign. But when it comes to the Supreme Court, normally nominees are approved or shot-down within about two months. So if the Senate doesn't jump on approval promptly, it will further reinforce their image of an obstructionist, do-nothing, party. And doing that, right now, will jeopardize a few seats in the upcoming election, which could damage their chokehold on the Senate and thus Congress. And the entirety of the House is up for election, as it is every two years, so it's possible that this could be the catalyst to flipping the House.
I think Obama's best chance of damaging the Senate is to put forth a moderate that they should have no significant reason to delay approval, just to prove their obstinate core.
The interesting thing about Scalia's death is what it does to cases that they've already decided but have not been published -- IT REMOVES HIS VOTE FROM THE TALLY. So any case that has been heard that had been decided by a 5-4 conservative vote are now likely 4-4 ties! It isn't a situation of ties go to the defender, but ties send it back to the lower court for reconsideration. After a deciding vote is taken, the Chief Justice assigns writing the decision to a justice, and it can be assigned to themselves. Anyone can write a supporting or dissenting opinion on their own as part of the record. And until the document is published, justices can change their vote! This makes a dissenting opinion in to a supporting opinion, and vice-versa.
And apparently this has happened, possibly as recently as the decision that supported the Affordable Care Act.
So the Senate has a real dilemma. If they delay a decision on what the public perceives as a well-qualified nominee just to be obstinate in hopes that a Republican, but not Trump, becomes President in November. Which means there's a vacancy on the Supreme Court of unheralded length, and also makes them look really bad. Or do they approve said nominee who may or may not toe the line of Republican ideology, whatever that happens to be at the moment.
Mitch McConnell has a lot to think about right now.
Another thing to consider is Justice Clarence Thomas. The observation is that Thomas always looked to Scalia for which way to vote. He's said about two sentences of dialog in the last decade in the Court, we have no way of knowing how vocal he is in private discussions at the Court. So what's he going to do? He can retire at any time, only time will tell if he starts asking questions as cases are heard, which could indicate that he can actually think for himself. Or he could remain the silent stoic and grab a new set of coattails to cling to.
I think the most interesting thing is that some justices, over the years, have proven that they're critical thinkers and not political ideologues. Sandra Day O'Conner was one, some of her votes were conservative-leaning and some were liberal. We've seen several decisions that stunned the punditocracy, including a conservative proving themselves to be a moderate in the Affordable Care Act decision.
Only time will tell.