On recess appointments in general and appointments to the Supreme Court specifically (2016). Difficult but Not impossible.

From teh blog:

It is true that one of the Justices regarded as a giant on the Court’s history, William J. Brennan, Jr., actually began his lengthy career with just such a short-term appointment. The chances of that happening again today seem to have diminished markedly.

The presidential authority at issue in this possible scenario exists, according to Article II, when the Senate has gone into recess and the vacancy a president seeks to fill remains. Such an appointment requires no action at all by the Senate, but the appointee can only serve until the end of the following Senate session. The president (if still in office) can then try again during a new Senate session, by making a new nomination, and that must be reviewed by the Senate.

The Supreme Court had never clarified that power until its decision in June 2014 in National Labor Relations Board v. Noel Canning.

https://www.senate.gov/CRSpubs/3d313cc2-9515-4533-b1f0-3f762cd09007.pdf

https://www.scotusblog.com/2016/02/is-a-recess-appointment-to-the-court-an-option/