On the eve of the Republican National Convention, President Obama published a piece in the Wall Street Journal lamenting "congressional inaction" on the nomination of Judge Merrick Garland to the Supreme Court. We have heard that term before, of course. Obama has often used congressional inaction on some issue (health care and immigration, most notably) to justify executive action: "We can't wait for Congress to do its job," he has said, "so where they won't act, I will."
But there is no "executive action" Obama can take to overcome "congressional inaction" on Garland's nomination—the Senate's refusal to take up the nomination and hold a hearing and have an up-or-down vote until after Election Day. The reason Obama has no such executive action available to him is the Constitution, which prescribes the appointment process for judges (and executive officers).
The president has the exclusive power to nominate a justice. He also has authority to appoint the justice. But that power is contingent on the Senate's exercise of its advice and consent power: The Senate must consent to the nomination or else there can be no appointment. Significantly, the Constitution does not say when or how the Senate is to exercise its authority.
The Constitution also provides that "the president shall have power to fill up all Vacancies that may happen during the Recess of the Senate, by granting Commissions which shall expire at the End of their next Session." Obama has shown no interest in using the authority duly granted him by that clause, declining to mention it in his op-ed. That's not surprising, since by making a recess appointment the president would be turning a lifetime appointment into one of no more than two years. In any event, the Senate can prevent the circumstance in which a president may lawfully make a recess appointment by holding pro forma sessions (in which business is rarely conducted) throughout a recess. An aide to Majority Leader Mitch McConnell confirmed that the Senate is doing that now, during the current recess.
Even on one of the last days of his presidency, Obama could appoint Garland. If Hillary Clinton wins, and Garland is still the nominee, the Republican Senate, preferring the judge to anyone Clinton might nominate, could confirm him in the lame duck session.
That seems unlikely. Majority Leader McConnell would have to change the position he has taken since the Senate first began blocking Garland's nomination. Which is that not Obama, but the next president—meaning Clinton or Trump—should get to choose Scalia's replacement.