CEDAR RAPIDS, Iowa — Dozens of reporters and photographers descended on the Hawkeye Downs speedway, all waiting for one man to appear at a local Labor Day picnic.

That man was not Michael Bennet.

“We’re having a great Labor Day in Iowa,” said Mr. Bennet, the Colorado senator and still a presidential candidate, showing up suddenly to address the scrum that gathered 20 minutes earlier for the arrival of Joseph R. Biden Jr. “And here comes the vice president! So let me get out of his way.”

Life isn’t easy these days for bottom-tier Democratic presidential candidates. Not many people know who they are. Fewer come to their events. No reporters cover them regularly.

The indignities don’t stop there. On Saturday, an Iowa Democrat approached a Wall Street Journal reporter and asked if he was Gov. Steve Bullock of Montana. “I don’t even have cowboy boots on,” the reporter, John McCormick, wrote on Twitter about the encounter. Mr. Bullock’s campaign didn’t have yard signs for a house party on Sunday, so it borrowed signs used by Andy McGuire in Iowa’s 2018 primary for governor and taped “Bullock” placards on them. (Ms. McGuire, who placed fourth in the primary, has endorsed Senator Amy Klobuchar of Minnesota for president.)