It's rope-a-dope. Graham is teasing the Dems to run Joe in 2020 because that's what he wants to happen. Pubs would love Biden vs. Trump. Graham is promoting Joe for that reason. Run Joe Run.
And if Hillary does 'jump in' at the last minute, all the Dems would release a collective dammit *sigh*, and they would all say together in unison,"Come on! Not this shit again!"
The Dems can beat Trump in 2020. The only problem is, they do not have any viable candidates. The DNC following are all liars, felons, illegals, homosexuals, Muslims, rich old White guys, super-billionaires, totalitarian Socialists, and other assorted weirdos. The DNC cannot find a normal, stable, contemporary candidate, because people like that are not Democrats. The Democrat Party is a magnet for crazy people. We saw that clearly in the two debates.