But the intruders failed to get past security defenses on the RNC’s computer networks, the officials said. And people close to the investigation said it indicated a less aggressive and much less persistent effort by Russian intelligence to hack the Republican group than the Democratic National Committee. Only a single email account linked to a long-departed RNC staffer was targeted…

The possibility that Russians tried and failed to infiltrate the RNC doesn’t necessarily conflict with the CIA’s conclusion. A senior U.S. official said analysts now believe what started as an information-gathering campaign aimed at both parties later took on a focus of leaked emails about Mrs. Clinton and Democrats…

Until now, few details had been disclosed about the nature of the targeting of Republican organizations, especially the flagship Republican National Committee, where hackers sent so-called phishing emails last spring to an email address there. Those emails were quarantined by a filter meant to detect spam as well as potentially malicious traffic that may carry viruses or trick recipients into divulging passwords, two officials said.

A third person familiar with the investigation said RNC staff members didn’t realize they had been the target of spies until June, after Democratic committee leaders revealed that hackers had successfully gained a foothold inside their networks. Once inside, they reportedly were able to access a trove of DNC opposition research on Mr. Trump, then a candidate.