Of course the US government is worried about cyber espionage leading to stolen sensitive data. However, another huge concern for the feds is the manipulation of that data so its integrity is called into question. This in turn leads to suspicion surrounding the legitimacy and accuracy of said data (emphasis added):

James Clapper, the director of national intelligence, told MSNBC last month “the next type of attack will involve deletion or manipulation of data as opposed to perhaps stealing it or denying service.” Jani Antikainen and Pasi Eronen, in an article on the Overt Action Web site, said that could result in the government not trusting its own personnel data, and therefore not its people.

Nothing is worse than the loss of trust.

“Suddenly, cleared personnel would have different relatives and some suspicious names in their ‘who do you know’ networks,” they wrote. “These unauthorized changes would thus deliver a massive blow to the trustworthiness of all data in the system….maliciously manipulating official forms and records on a large scale would turn them toxic and into a source of great mistrust.”

Clapper’s office has warned employees they could be hit by various social engineering tools “bad actors” could use “to gain your trust and extract further information or manipulate you to take actions you would not otherwise take.”

The social engineering tools include phishing (for example, using an e-mail attachment to install malicious software), social media deception and human targeting.

Let me repeat that: nothing is worse than the loss of trust. Forget ever handling classified material again once that trust is broken.