I'll give you my take. I think McCain had "something" on Lyndsey, something that he held over his head that Lyndsey was terrified would get out. Pure blackmail.
I think Lyndsey's observed the Trump phenomenon, and learned that no matter the personal "scandal", conservatives can and will forgive personal indiscretions if you fight back against the over-arching tyranny of liberalism.
I think Lyndsey's in the process of rebuilding his conservative "street cred" in the event his "secret" makes it's way out.
But I also think this is closer to the real Lyndsey Graham, because he's having waaaaayyyy too much fun doing it.
Lindsey was this way during the Clinton impeachment. I loved the guy. McCain ruined Graham just as he ruined everything he touched during his miserable existence.
Perhaps.
He does seem to be more authentic and swift with the sly replies lately.