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Campaign aides for Senator Bernie Sanders of Vermont said Monday night that the Democratic Party did not collect the results of 90 Iowa precincts, which is about 5 percent of all votes cast in the state, because the party had failed to properly staff the precincts.

Rania Batrice, a spokeswoman for the campaign based in Iowa, said that the party reached out to the campaigns of Mr. Sanders and Hillary Clinton and asked them to help tally the results. “It’s just offensive that they dropped the ball like this,” she said. “It’s ridiculous.”

Monday night it was unclear how the issue would be resolved.

Ms. Batrice said the party was supposed to properly staff all precincts with caucus chairs but that some of those people responsible for calculating the results did not shown up.

The Democratic Party pushed back against reports that the caucus sites were not staffed appropriately.

“We are currently getting results from our small number of outstanding precincts, and results continue to be reported on our public website,” the party said in statement. “These outstanding precincts have chairs who we are in the process of contacting to get their results. It is inaccurate to report that these precincts did not have chairs.”

The party said that it was seeking help from the campaigns in contacting their precinct chairs.