Joe Biden may have just received the worst news of his campaign, as a new poll shows his support in his firewall state of South Carolina collapsing along with his once-dominant support among black voters, with Vermont Sen. Bernie Sanders and Tom Steyer closing the gap.

Biden's support in South Carolina had held steady all campaign season, and the hope was that it was strong enough to allow him to survive early defeats in Iowa and New Hampshire and pull off a big win ahead of Super Tuesday when the largest single-day haul of delegates is available. If the new Post and Courier-Change Research poll is right and his lead is evaporating, then it puts much more pressure on him to win either Iowa or New Hampshire.

While the poll shows Biden still in the lead, he's at just 25%, with Sanders at 20% and Steyer (who has carpet-bombed the state with TV ads) at 18%. Biden once led in the poll by as high as 31 points.

Especially alarming for Biden is that he's down to 30% support among black voters, who make up two-thirds of the South Carolina electorate and are a crucial voting bloc in the later states. Last summer, Biden captured half of black voters. Steyer is now at 24% among black voters, with Sanders at 16%.

If this is what's happening in South Carolina now, imagine if Biden loses Iowa and New Hampshire to Sanders, a very real possibility. Were that to happen, it would seriously damage his electability argument, going into a must-win state.

The flip side of this is that it's fantastic news for Sanders, who has narrowed the gap enough in South Carolina, that he could conceivably close it if he gains momentum from early wins in Iowa and New Hampshire.

It's time for Democratic elites worried about a Sanders nomination to panic.