A Secret Service source explains that Matthew Goldstein, 55, got caught up in traffic-circle confusion during the heavy afternoon rush in downtown D.C.
Unfamiliar with the traffic pattern, he apparently panicked and made a sharp right turn that put him immediately behind a group of cars, which turned out to be a White House motorcade.
The IRS computer worker drove along behind those vehicles carrying President Barack Obama's two daughters and rolled right through a perimeter barricade on Pennsylvania Avenue.
But how did the Secret Service let him through?
The guards apparently didn't have time to raise the bollards fast enough to shut Goldstein's car out. But he was stopped immediately and then was arrested.
He faces a misdemeanor count of unlawful entry and was due in court on Wednesday. However, the source said it appears to be an honest error on the driver's part.
The breach prompted a temporary lockdown of the White House complex where Obama was meeting with Secretary of State John Kerry.