Only one candidate has dropped out of the Democratic race so far — Rep. Eric Swalwell of California. He took part in the first debate, but remained at an unmeasurable level in the polls. “We have to be honest about our own candidacy’s viability,” Swalwell said in announcing his departure.

Soon other candidates will have to reach that same level of honesty. If they don’t make the cut for the September debate, they’ll be instantly robbed of their only opportunity to reach a nationwide audience, and they’ll be just as instantly relegated to the category of also-ran.

Republicans had a big field — 17 candidates — in 2016. They, too, started dropping out early. Back then, the first GOP debate was held on August 6, 2015, the second on September 16, and the third on October 28 — all months before the first primary or caucus votes.

Rick Perry dropped out between the first and second debates. Scott Walker dropped out a few days after the second debate. Bobby Jindal dropped out after the third, as did, later, Lindsey Graham and George Pataki.