The debate stage before a 2016 Democratic primary debate hosted by NBC and YouTube in Charleston, S.C. Candidates will need higher poll numbers and more grassroots donors to participate in later debates this year.

The debate stage before a 2016 Democratic primary debate hosted by NBC and YouTube in Charleston, S.C. Candidates will need higher poll numbers and more grassroots donors to participate in later debates this year.

The debate stage before a 2016 Democratic primary debate hosted by NBC and YouTube in Charleston, S.C. Candidates will need higher poll numbers and more grassroots donors to participate in later debates this year.

The debate stage before a 2016 Democratic primary debate hosted by NBC and YouTube in Charleston, S.C. Candidates will need higher poll numbers and more grassroots donors to participate in later debates this year