Washington (CNN) Long before the polls close in New Hampshire on Tuesday night -- 8 p.m. Eastern if you are wondering -- Joe Biden was gone from the Granite State.

He left New Hampshire in the late afternoon Tuesday to fly to South Carolina, the state that he has repeatedly called his "firewall."

Here's the problem for Biden: The South Carolina primary is not until February 29 -- 18 days from now.

There will be one vote between Wednesday and then (the Nevada caucuses on February 22) and two debates (one February 19 in Las Vegas, the other February 25 in Charleston). Those are rightly understood as oases in the broader political desert that sprawls out before Biden right now.

While there's little question that Biden will stay in the race through South Carolina, it's also true that he will do so facing two constant questions each of the next 18 days:

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