Like Miami, which hosted the Democrats’ first debate in June, Houston was among the final group of cities considered to host next year’s Democratic convention. (Milwaukee eventually took the prize.) The choice of Texas could also be seen as a statement of intent by the party to be competitive in a state that has not been won by a Democratic presidential candidate since 1976.

The last time that Democrats hosted a presidential primary debate in Texas was in February 2008, when Barack Obama and Hillary Clinton met in Austin at an event sponsored by CNN and Univision.

The third debate, which will pre-empt ABC’s usual weeknight programming, is expected to include a more condensed version of the current, sprawling Democratic field. A total of 20 candidates appeared over two nights in Miami last month, and 20 are expected for the second Democratic debate in Detroit in July, which will also be split between two nights to accommodate the number of contenders.

But Democratic officials tightened requirements for the ABC debate, raising the threshold that candidates must meet for national polling performance and the number of unique donors to their campaigns.

Ratings for the first Democratic debate in Miami, hosted by NBC, MSNBC and Telemundo, exceeded industry expectations. The June 28 event — which featured a clash between Senator Kamala Harris of California and former Vice President Joseph R. Biden Jr. — was seen live by about 18 million Americans, a record for a Democratic primary debate and a sign of intense early engagement with the 2020 race.