Just to be clear, they were mediocre when they were hired - they didn't become mediocre while working there.
Here's a just a few of their more notable screwups.
November 2009: A Washington couple, Tareq and Michaele Salahi, crash Obama’s first state dinner. The Secret Service later acknowledges that officers never checked whether they were on the guest list.
November 2011: A man with a semiautomatic rifle parks in front of the White House and fires at the building, with Sasha Obama inside and Malia Obama on her way home. The Secret Service does not figure out that shots hit the building until contractors detect the bullets in the outside woodwork some time later.
April 2012: Eight Secret Service in Colombia lose their jobs after they took prostitutes from a strip club back to their hotel rooms. A Justice Department investigation finds that two Drug Enforcement Administration agents arranged one encounter between a prostitute and a Secret Service officer.
May 2013: A Secret Service supervisor leaves a bullet in a woman’s room at the Hay-Adams hotel, which overlooks the White House, and allegedly tries to force his way into the room to retrieve it.
December 2013: A man who stood close to President Barack Obama and other heads of state while providing sign language interpretation at Nelson Mandela’s memorial was a fake who was making up his own gestures, sign language experts say, raising questions about the security at the event.
March 2014: Three Secret Service agents responsible for protecting Obama in Amsterdam are placed on leave after a night of drinking, in violation of Secret Service rules. One of the agents passed out drunk in a hallway.
September 2014: A security contractor with a gun and an assault record got on an elevator with the president during a trip to Atlanta. The contractor used his cellphone to take video of Obama and did not stop when Secret Service agents told him to. The Secret Service only learned that the man has a gun after he was fired on the spot and turns it over.
September 2014: An man with a knife jumps the White House fence, dashes through the North Portico doors and makes it deep inside the building, into the East Room, before he is tackled, and only then by an off-duty Secret Service agent. A security alarm was disabled because staff nearby found it too noisy.
March 2015: Two senior agents hit a security barrier near the White House in a government vehicle. The men had been out drinking, celebrating the retirement of the agency's spokesman. When they reached the White House, their car barreled through temporary barriers blocking an active bomb investigation and they may have even driven over the suspicious package.
June 2015: A Secret Service officer in the Uniformed Division had his gun stolen from his personal car after parking it outside his girlfriend’s condo in Adams Morgan.
2022: Two men impersonated Federal agents while living in a penthouse apartment in Washington, D.C.'s Navy Yard paid for by DHS, and compromised U.S. Secret Service personnel involved in protective details. Arian Taherzadeh and Haider Ali had been offering free apartments and other gifts to U.S. Secret Service agents and officers. FBI agents also found a machine to create and program personal identification verification cards which can be used to access sensitive law enforcement computers. Taherzadeh and Ali had falsely claimed to work for the Department of Homeland Security on a special task force investigating gangs and violence connected to the Jan. 6 "insurrection" at the U.S. Capitol. They provided Secret Service officers and agents with rent-free apartments, including a penthouse worth over $40,000 a year, along with iPhones, surveillance systems, a drone, a television, a generator, a gun case and other policing tools. The investigation into these two only began when they were witnesses to an assault involving a letter carrier and Postal Inspection Agents interviewed them. The USPIS Inspector provided this information to the DHS Office of Inspector General, which then referred the information to the FBI for further investigation.
April 2023: An intruder entered the home of national security adviser Jake Sullivan undetected.
Right. I meant “have become” in the context of today’s government workers vs. the ones from several decades ago.