Cory Booker, Kamala Harris, Pete Buttigieg and Elizabeth Warren. Photos: Scott Olson/Getty Images, Jim Watson/AFP/Getty Images, and Brendan Smialowski/AFP/Getty Images

The fourth round of Democratic debates will be held on Oct. 15 in Westerville, Ohio, with 12 candidates onstage, making it the biggest single-night debate to date. 

How it works: This debate had the same requirements as September's. Qualifying candidates must have reached 2% in 4 DNC-approved polls and drawn 130,000 unique donors — including 400 donors in 20 different states. Oct. 1 was the final day to make the cut.

Why it matters: The Democrats' massive 2020 field has put pressure on the DNC to focus its primary on those who can really challenge President Trump.

Which candidates will be on stage:
  1. Sen. Amy Klobuchar
  2. Sen. Cory Booker
  3. Mayor Pete Buttigieg
  4. Sen. Bernie Sanders
  5. Former Vice President Joe Biden
  6. Sen. Elizabeth Warren
  7. Sen. Kamala Harris
  8. Entrepreneur Andrew Yang
  9. Former Rep. Beto O'Rourke
  10. Former HUD Secretary Julián Castro
  11. Billionaire and activist Tom Steyer
  12. Rep. Tulsi Gabbard
Candidates that had at least 130,000 donors but did not meet the polling threshold:
  1. Author Marianne Williamson
Candidates who did not meet any qualifications for Ohio:
  1. Mayor Wayne Messam
  2. Former Rep. Joe Sestak
  3. Former Rep. John Delaney
  4. Rep. Tim Ryan
  5. Sen. Michael Bennet
  6. Gov. Steve Bullock

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Editor's note: This piece has been updated to reflect recent DNC requirement changes for the October debate.

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