The gunman who sprinted through a security checkpoint on Saturday night at the Washington Hilton believed that the Secret Service was poorly prepared to guard top administration officials against him, according to writing he left behind. Agents, in turn, stopped him in a matter of seconds.

The episode raised fresh questions about whether the Secret Service was sufficiently prepared to protect the president in an age of rising threats and spasms of political violence. But officials insisted that the security measures had worked as intended, pointing to the fact that the suspect never made it into the hotel ballroom where President Trump and hundreds of journalists were gathered for the White House Correspondents’ Association dinner.

“The system worked,” Todd Blanche, the acting attorney general, said in an interview on NBC’s “Meet the Press” on Sunday, recounting how the suspect made it only feet past the security perimeter.

The suspect’s writing was shared with The New York Times by two law enforcement officials who spoke on the condition of anonymity to disclose the information.

Even as some politicians and pundits contended on Sunday that security should have been tighter and that the suspect should never have gotten that close, former law enforcement officials said in interviews that the appropriate safeguards appeared to have been in place.

“From experience, this could have been a massacre,” said Paul Eckloff, who served on President Trump’s security detail during his first term. “It wasn’t, because armed, trained professionals stood between the attacker and a ballroom full of people. The question is not, how did he get close? The question people should be asking is, why is everyone alive? It’s because the security plan worked.”