Many Democratic presidential candidates on Sunday called for the release of the special counsel’s entire report and said they were dissatisfied with relying on Attorney General William P. Barr’s four-page summary of the two-year investigation.

Mr. Barr’s letter said the investigation, led by the special counsel, Robert S. Mueller III, concluded that neither the president nor his aides conspired or coordinated with the Russian government in its interference in the 2016 presidential election.

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Julian Castro, one of the 15 Democrats to have announced their candidacy for president in 2020, said Congress should be allowed to see the report in its entirety. He said Mr. Barr was too close to the Trump administration for his summary to be the only peek into Mr. Mueller’s work.

“A politically appointed Attorney General shouldn’t decide how much of the Special Counsel report Congress can read,” Mr. Castro tweeted minutes after the letter was released. “The full report should be released and Robert Mueller should testify to its findings.”