Joe Biden thinks he has the crucial South Carolina Democratic presidential primary in the bag.

Um, truth be told, he doesn’t. Even if he wins, it’s not tucked away. He’s got to win by a lot. You see, the one-time Democratic Party presidential frontrunner had the Palmetto State primary locked up. He was lapping the field. Then Vermont’s independent Sen. Bernie Sanders started winning the early primaries.

Now it’s neck-and-neck between the two of ’em for South Carolina’s primary vote.

Biden said that a single percentage point victory over the field is enough, although he said he expects to win by a comfortable margin. OK, but expectations and reality don’t always mesh.

The former vice president of the United States needs to win by at least double digits. It would be better for him to smoke the field, to trample the rest of the remaining contenders — and that includes Sanders — into the ground.

Anything short of a decisive win spells doom.

It saddens me to say this, as I have staked my own preference on Joe Biden. I want his candidacy to succeed. I fear it’s teetering on the brink of failure.