Civil rights leader Jesse Jackson says that another candidate might have to enter the presidential race to "fill the gap" if Clinton and Brown fail to appeal to the voters.
"There is concern about ... the large number of registered voters not voting. This does reflect some dissatisfaction," Jackson told reporters.
"There's a gap, and nature and politics abhor gaps. Either those who are running will fill those gaps, or somebody not running will fill the gap," said Jackson. He did not elaborate.
But Jackson, a two-time candidate for president, said he still does not plan to run.
Jackson was attending an "urban summit" of 13 US mayors and the two Democratic candidates, who face the New York primary on April 7.
Jackson, who commands the loyalty of millions of black voters, suggested he was personally dissatisfied with both candidates and said they were spending too much time "throwing spears at each other."