If the true source was the CIA and Libby wanted to mask that, a corrupt endeavor would be a desire to trick the investigators into thinking the information was derived from reporters. The motive being that unless he deflects the real source he might be guilty of a possible crime.
However, if the true source was not the CIA but actually was a reporter then can a corrupt endeavor occur? He no longer is motivated by hiding the truth of his source.
"True source" being what? Of Libby's knowledge or belief? Or of "the leak?"
The false statement charge is the based on the former - that Libby had knowledge or belief from inquiry of the CIA, but Libby tried to hide that the source of his knowledge or belief from investigators. Instead, alleges the indictment, Libby tried to mislead investigators to the conclusion tha Libby obtained his belief from contact with reporters.
However, if the true source was not the CIA but actually was a reporter then can a corrupt endeavor occur?
If the fact pattern is changed so that Libby did not have any knowledge of Plame except what he heard from reporters, then the indictment could not be brought. The indictment depends on Libby having knowledge of Plame independently from conversations with reporters.