Final answer:
Presidents have historically worried about events like major leaks of classified information, security breaches, and potential terrorist threats, as exemplified by Nixon's Watergate scandal and the security measures adopted after the September 11 attacks.
Step-by-step explanation:
Two events that have historically caused presidents to worry about the White House include major leaks of classified information and security breaches, as well as potential terrorist threats. For instance, during President Nixon's term, the Watergate break-in, which was a burglary at the Democratic headquarters by Nixon's supporters, ultimately led to his resignation due to the cover-up of the crime. It was a significant security breach and abuse of presidential power that worried the administration and contributed to a loss of faith in the political system. Additionally, the September 11 terrorist attacks during President George W. Bush's tenure created a great concern for domestic security and led to sweeping changes such as the creation of the Department of Homeland Security and the implementation of the USA Patriot Act to prevent future attacks.