The director of the Secret Service resigned Tuesday in the aftermath of the assassination attempt on former President Donald Trump that unleashed an outcry about how the agency failed in its core mission to protect current and former presidents.

Kimberly Cheatle, who had served as Secret Service director since August 2022, faced growing calls to resign and several investigations into how a gunman was able to get so close to the Republican presidential nominee at an outdoor campaign rally in Pennsylvania.

“I take full responsibility for the security lapse,” she said in an email to staff obtained by The Associated Press. “In light of recent events, it is with a heavy heart that I have made the difficult decision to step down as your director.”

Cheatle's departure was unlikely to end the scrutiny of the long-troubled agency after the failures of July 13, and it comes at a critical juncture ahead of the Democratic National Convention and a busy presidential campaign season. Lawmakers on both sides of the aisle have promised more investigations. An inspector general probe and an independent, bipartisan effort launched at President Joe Biden's behest will keep the agency in the spotlight.

Cheatle's resignation came a day after she appeared before a congressional committee and was berated for hours by both Democrats and Republicans for the security failures. She called the attempt on Trump's life the Secret Service's “most significant operational failure” in decades, but she angered lawmakers by failing to answer specific questions about the investigation.

Biden said in a statement that “what happened that day can never happen again,” and he planned to appoint a new director soon, but he did not discuss a timeline.

The president and Homeland Security Secretary Alejandro Mayorkas thanked Cheatle for her service. Mayorkas appointed Deputy Director Ronald Rowe as acting director. He has worked for the agency for 23 years.

At the hearing Monday, Cheatle remained defiant that she was the “right person” to lead the Secret Service, even as she said she took responsibility for the failures. When Republican Rep. Nancy Mace suggested Cheatle begin drafting her resignation letter from the hearing room, Cheatle responded, “No, thank you.”

The 20-year-old shooter, Thomas Matthew Crooks, was able to get within 135 meters (157 yards) of the stage where the former president was speaking when he opened fire. That's despite a threat on Trump's life from Iran that led to additional security for the former president in the days before the rally.

Cheatle acknowledged Monday that the Secret Service was told about a suspicious person two to five times before the rally shooting. She also revealed that the roof from which Crooks fired had been identified as a potential vulnerability days earlier. But she failed to answer many questions about what happened, including why there were no agents on the roof.

A bloodied Trump was quickly escorted off the stage by Secret Service agents, and agency snipers killed the shooter. Trump said part of his right ear was pierced in the shooting. One rallygoer was killed, and two others were critically wounded.

Details continue to emerge about signs of trouble that day and the roles of the Secret Service and local authorities. The agency routinely relies on local law enforcement to secure the perimeter of events. Former top Secret Service agents said the gunman should never have been allowed to gain access to the roof.

After Cheatle's resignation, Trump posted on his social media network: “The Biden/Harris Administration did not properly protect me, and I was forced to take a bullet for Democracy. IT WAS MY GREAT HONOR TO DO SO!”

The House Homeland Security Committee had asked Cheatle to testify Tuesday for another hearing on the assassination attempt, but lawmakers said she refused. Cheatle's name was on a card on a table in front of an empty chair during the hearing, which began shortly before her decision to step down became public.

The Secret Service is a part of the Department of Homeland Security, which includes immigration, transportation security and the Coast Guard. The department was formed after the Sept. 11, 2001, terrorist attacks.