Reporting from Sioux City, Iowa — Joe Sanberg was a bit flummoxed. He was trying to list all the Democrats running for president and, after naming 12 in fairly quick succession, was temporarily stuck. “Holy smokes,” he muttered, “who am I missing?”

After 2 minutes and 25 seconds, the Los Angeles-based investor identified the whole field, 18 at the time. The candidates, like cells in a petri dish, have multiplied further since, but even with 23 contenders, Sanberg thinks there just might be room for one more.