Clinton was wrong: Lewinsky did not threaten national security.
Petraeus was wrong: his paramour may have had access to national security material.
And you think Lewinsky didn't have access to national security material?
Considering that she was just an intern, she may have had access to certain classified documents, but nothing concerning national security. Those briefings are brought in to the President and then taken away when they leave, or he goes to the Pentagon to receive the news.
Apparently you don't know much about how the classified system works. I do, I was a Personnelman for 20 years in the U.S. Navy from 1982 until 2002.