The African-American vote, usually an afterthought until after the Iowa and New Hampshire primaries, is now one of the biggest factors in the Democratic primary.

The campaigns of both Hillary Clinton and Vermont Sen. Bernie Sanders see the support of blacks as crucial to their paths to the nomination, and the potential entrance of Vice President Biden looms as a huge unknown, as Biden would also aggressively compete in heavily-black areas if he becomes a candidate.

Having already surged in Iowa and New Hampshire because of his support from white liberals, Sanders is trying hard to appeal to African-Americans and rebut the idea that he is a candidate with a narrow, white-only support base. Clinton’s aides, acknowledging the rise of Sanders, are reassuring her nervous supporters by emphasizing the former secretary of state’s huge lead over Sanders among black and Hispanic voters, who are a larger part of the electorate after Iowa and New Hampshire.

And Clinton is taking steps to shore up that support among African-Americans. The former secretary of state did an interview on Friday with American Urban Radio, then will fly on Saturday from New Hampshire to Washington, D.C. to host a reception for those attending the Congressional Black Caucus's annual conference.

On Monday, Clinton will campaign in Louisiana and Arkansas, which hold primaries in March 2016, after the early votes in states like Iowa, New Hampshire and South Carolina. In 2008, about half of the voters in the Louisiana Democratic primary were black.

Asked in an interview Thursday by CNN about Sanders’ rise in polls in Iowa and New Hampshire, Clinton defended her performance in those states, but added, “we’re moving on to the states that come after.”

Meanwhile, allies of Biden say if he runs for president, he will bank on winning South Carolina, a state where he has vacationed often for the last seven years at Kiawah Island near Charleston and maintains deep ties with local Democratic leaders. A win in South Carolina by Biden will require strong black support, since about half of the Democratic voters there are African-Americans.

And Biden, if he runs, is likely to cast himself as the heir to President Obama, who remains deeply popular among black voters. Biden also attended the black caucus conference on Saturday morning, not giving a speech but spending more than two hours at a breakfast there shaking hands and posing for pictures. On stage, the CBC's chairman, U.S. Rep. G.K. Butterfield of North Carolina, called Biden a "longtime CBC friend."

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“If Biden ran, he would get the black vote. No question,” said one former Obama aide, who worked on the president’s 2008 and 2012 campaigns. “People have already voted for him twice.”

This aide said he met recently with Biden and urged him to enter the race.

Rick Wade, a South Carolina political operative who oversaw black outreach there and nationally in Obama's 2008 campaign, said, "Biden could do well in South Carolina, he has a strong history here."

Sanders’ ascent in Iowa and New Hampshire, states where fewer than 5 percent of people are black, has both allowed him to start concentrating on other states and heightened his need to, as he now appears a viable candidate who could win the Democratic nomination. And his campaign is aware of both his low polling among blacks and a perception problem from incidents over the summer when he appeared to be annoyed by protesters from the “Black Lives Matter” group.

So over the last few weeks, the senator has campaigned in South Carolina with the author and activist Cornel West, including a stop at Benedict College, a historically black school in Columbia. He has held meetings with members of the Congressional Black Caucus and Campaign Zero, a new initiative run by some of the Black Lives Matter activists that is aiming to end police shootings of citizens. And Sanders increasingly speaks in pointed ways about the legacy of racial discrimination in America, mostly notably in a recent speech in which he suggested that the U.S. was founded on “racist principles.”

In South Carolina, Sanders’s campaign is now greatly expanding its number of canvassers. And in states with later primaries, Sanders’ aides say he could woo black voters who are demographically-similar to the senator’s white supporters: those who are younger and well-educated. African-Americans under 30 are too young to have voted to put Bill and Hillary Clinton in the White House in the 1990’s, while Sanders deeply-progressive views may appeal to black liberal college graduates in states like Georgia, which also has a March primary.

“I think we’re going to do a lot better than people think in states like South Carolina,” Sanders told MSNBC’s Rachel Maddow in an interview on Thursday night.

Biden has taken no serious steps to run. But if he opted to enter the race, he would likely have the implicit, if not direct support of South Carolina U.S. Rep. James Clyburn, a member of the Democratic leadership in the House and one of the most influential African-Americans in Congress. The congressman feuded with the Clintons during the 2008 campaign and has not endorsed the former first lady in this race.

“Joe Biden has a lot of support in South Carolina, always has,” Clyburn recently told Politico. In a speech last year, Clyburn suggested Biden was the “most important vice-president in history.”

Most polls of the 2016 Democratic field currently show Clinton carrying a majority of black votes nationally and in South Carolina, with Biden trailing and Sanders very far behind. A dozen members of the CBC, including New Jersey Sen. Cory Booker, have already endorsed her. Many of the top African-American staffers in Democratic politics are on her staff, such as former Democratic National Committee communications director Karen Finney and Marlon Marshall, who was Obama’s deputy field director in 2012.

Clinton took a number of early steps in her campaign to connect with African-Americans, such as giving major speeches on criminal justice reform and expanding voting rights, as well as visiting the Ferguson, Missouri area.

Clinton' s June speech on creating universal, automatic voter registration made her "the first person in the campaign to really talk about that," said Maya Harris, one of Clinton's top policy advisers.

But the big question is how solid that black support would remain for Clinton if Biden entered the race or if Sanders starts to build a following in the black community. Polls now suggest Sanders is much less well-known among black voters compared to Biden or Clinton.

And Clinton has had strong black support before only to watch it wither away.

During much of 2007, the former first lady was ahead Obama or at least a strong second in polls of African-American voters. About half of the members of the Congressional Black Caucus backed Clinton, not Obama, with most of them citing their long relationships with Hillary and Bill.

But when people actually cast their ballots, Clinton received less than 20 percent of the black vote in primaries in the South, preventing her from winning those states. Seeing Obama’s deep support in the black community, some of Clinton’s supporters, such as Georgia U.S. Rep. John Lewis, switched to the then-Illinois senator.

Obviously, in 2016, Clinton will not be running against a candidate who could become the first black president. But the results of 2008 suggest Clinton’s early advantage with blacks is not ironclad.