The image seemed swiped from a far-fetched film: a President demanding to be taken to the chaos at the Capitol, and a Secret Service agent insisting on ferrying the commander in chief back to the West Wing. In a rage, the chief executive lunges for the steering wheel of his sport utility vehicle, believing his date with destiny awaits in Congress’s sacked home.

The testimony of a one-time White House staffer, Cassidy Hutchinson, before the January 6 committee was replete with vivid details, none more so than that picture of President Trump lunging for the steering wheel and the “clavicles” of a Secret Service agent, Robert Engel. The truth, it seemed, was stranger than even the most audacious fiction. 

Was it the truth? In the hours following Ms. Hutchinson’s testimony, the chief White House correspondent for NBC News, Peter Alexander, tweeted that both Mr. Engel and the vehicle’s driver “are prepared to testify under oath that neither man was assaulted and that Mr. Trump never lunged for the steering wheel.”

Ms. Hutchinson’s attorney, Jody Alexander, responded that his client “testified, under oath, and recounted what she was told. Those with knowledge of the episode also should testify under oath.” Ms. Hutchinson did not witness this episode first-hand. 

She reports having learned of it from the White House’s head of security, Tony Ornato. CBS and others report that Messrs. Engel and Ornato have both testified before the committee, albeit in private. Their testimony was not played in the hearing, though pressure is likely to increase to hear from them. The committee plans to next convene in July.

The Secret Service’s spokesman, Anthony Gugliemi, told the NBC correspondent that its agents are “available to testify under oath, responding to [Ms. Hutchinson’s] new allegations.” Mr. Alexander suggests that the testimony would confirm an irate president demanding to be taken to the Capitol, but not the lunge for the wheel. 

This turn in the spotlight is a departure for an agency accustomed to working in the shadows. Founded in 1865 to battle the widespread counterfeiting of currency in the wake of the Civil War, the Secret Service was until 2003 under the auspices of the Department of the Treasury. That year, it migrated to the then newly formed Department of Homeland Security.

The Secret Service’s mandate is prescribed by federal statute, which directs its agents to protect, among others, “The President, the Vice President (or other officer next in the order of succession to the Office of President), the President-elect, and the Vice President-elect.” By law, this protection cannot be refused.

It’s unclear, at least to the Sun, whether the Constitution permits Congress to curb the president’s authority over executive branch departments. The reported tension between Mr. Trump and his security detail underlines the peculiarities of an executive branch agency charged by Congress to tell the chief executive where it’ll permit him to carry out his duties.

An attorney and one-time professor at Virginia Commonwealth university, Matthew Pinsker, tells the Sun that in a situation such as the one described by Ms. Hutchinson, the agent’s job is to “guard the president’s life,” a mission that is “about the position, not the person.” Where Congress gets the power to direct an executive branch agent is not apparent in the parchment.

Even if, as reported, the president ordered his security detail to head to the Capitol, Mr. Pinsker believes that the agent would be required to disobey such a command if it would pose undue risk. He compares it to the military directive to “obey lawful orders and regulations that are issued,” which allows for exceptions of insubordination if an order is not lawful.

The Secret Service’s most notable failure also involved a president in a car. On November 22, 1963, President Kennedy was gunned down at Dallas. JFK was notoriously reckless with his personal safety, telling a spokesman, “If anyone is crazy enough to want to kill a president of the United States, he can do it,” an invitation taken up by Lee Harvey Oswald.  

After President Kennedy’s brother, Robert, was assassinated in 1968, Congress greenlit protection for presidential and vice presidential candidates and nominees. On January 6, 2021, the Secret Service was responsible for evacuating Vice President Pence during the riot. 

Keeping faith with its original charter, the Secret Service is also “authorized to detect and arrest any person who violates” certain species of financial crimes, including “any of the laws of the United States relating to coins, obligations, and securities of the United States and of foreign governments.”    

A 2012 report by Bloomberg found that the Secret Service accepted less than 1 percent of job applicants. Nevertheless, it has not been spared its share of embarrassment. Just last month, two agents were sent home from Seoul in advance of a presidential visit after “an off-duty incident involving two employees which may constitute potential policy violations.”

Most embarassing of all was a 2012 presidential trip to Cartagena, which rocked the agency with allegations that at least a dozen agents had engaged in heavy drinking and employment of prostitutes. In 2014, a man jumped the White House fence and was able to penetrate the executive mansion.

In April, four Secret Service agents were, according to the Washington Post, “allegedly hoodwinked by two men impersonating federal agents and plying them with gifts.” One of those men had recently traveled to Iran and Pakistan. 

As Carol Leonnig surveys this string of failures in her definitive history of the Secret Service, “Zero Fail: The Rise and Fall of the Secret Service,” she relates her assessment that “this long-revered agency was not living up to its most solemn duty — to keep the president safe.”

There were less solemn duties as well, as Mrs. Leonnig notes that when it came to JFK, agents “stood witness to a steady parade of secretaries, starlets, and even prostitutes escorted to the president’s bedroom — in hotels and in his private residence. The Secret Service agents weren’t allowed to ask the women’s names.”

It increasingly looks like agents will not be asking questions but instead answering them under oath. Even for an agency accustomed to pressure, the stakes are high.