Candidates must also amass donations from at least 200,000 unique donors, with a minimum of 800 donors in 20 states, territories or Washington, D.C.

Those standards are steeper than the criteria candidates are required to meet to partake in the upcoming November debate. To appear in that forum, candidates only need to achieve at least 3 percent support in four qualifying polls and receive contributions from 165,000 donors.

After the debate earlier this month in Westerville, Ohio, saw a dozen candidates jostling for speaking time, the increasingly challenging thresholds are sure to strain some of the lower-performing campaigns.

The December debate will air live on PBS and will be streamed online on POLITICO’s and PBS NewsHour’s digital platforms. The format and moderators will be announced at a future date, the DNC said in a statement.

"We are thrilled to partner with PBS Newshour for the final Democratic Presidential debate of 2019," said Patrick Steel, CEO of POLITICO. "On the cusp of a hugely consequential election year, we cannot think of a better place than California to demonstrate the breadth of POLITICO’s platforms and reach, as we expand our coverage and overall footprint in California and across the states."

Sponsors of the four previous primary debates included NBC, MSNBC and Telemundo in June; CNN in July; ABC News and Univision in September; and CNN and The New York Times in October.

Nine candidates have so far qualified for the Atlanta-area debate on Nov. 20, which is being co-hosted by MSNBC and The Washington Post.