CNN's 2020 Democratic debate set for July 30-31.

(CNN) — The second debate of the 2020 Democratic presidential primary, hosted by CNN, will take place in Detroit on July 30 and 31, the Democratic National Committee announced Tuesday.

The debate will bring the crowded field of Democratic candidates to the battleground state of Michigan, which President Donald Trump won in 2016.

The debate will feature randomized lineups drawn from a maximum of 20 qualifying candidates. A total of 12 presidential primary debates are planned during the 2020 cycle. The first debate, hosted by NBC News, will be June 26-27 in Miami.

The 2020 Democratic field is already large and diverse, with more than a dozen contenders in the race and other high-profile candidates, including former Vice President Joe Biden and Georgia Democrat Stacey Abrams, still considering a run.

Qualifying for the debates is based on a two-path system, determined by polling and grass-roots fundraising. The selection methodology will use the two measures in combination if more than 20 candidates qualify and the field needs to be narrowed down.

The debate will be over two days because the field is too big to fit on one stage. The Democratic National Committee will pick at random who ends up on each day. Up to 10 candidates will be onstage each night, so if there are more than 20 Democrats running, those who have not reached the threshold for grass-roots fundraising or polling will be excluded from the debate.

According to the debate guidelines, candidates "may qualify for the debate by registering at 1% or more support in three separate polls (either national polls or polls of the electorate in Iowa, New Hampshire, South Carolina and/or Nevada) publicly released between January 1, 2019, and 14 days prior to the date of the debate," with "qualifying polls" coming from a DNC-approved list. That list includes polls from the Associated Press, ABC News, CBS News, CNN, Des Moines Register, Fox News, Las Vegas Review-Journal, Monmouth University, NBC News, New York Times, NPR, Quinnipiac University, Reuters, University of New Hampshire, Wall Street Journal, USA Today, Washington Post and Winthrop University.

The three polls used by candidates to qualify for the debate must be from three different organizations, or the same organization but of different geographical areas.

In addition to the polling criteria, candidates may qualify if they have received campaign contributions from at least 65,000 unique donors, and a minimum of 200 unique donors per state in at least 20 US states.