Sessions was addressing two issues with leaks, some of them overlap. When classified information is leaked, it directly hurts the security of the country. That's one type of leak. The other leak relates to confidential discussions that may or may not be classified but would damage America's ability to conduct foreign affairs if leaked. For example, how would your Prime Minister feel if his private conversation with the President about relations between America and the Netherlands were printed word for word in the next morning's newspaper. Foreign leaders would not want to talk to the American government about important matters. We couldn't conduct affairs between us. That hurts relations between our countries and could have security implications, as well.
There are all sorts of leaks, for all sorts of reasons (some intentional). That has nothing to do with the free media and their right to keep their sources undisclosed, otherwise, their work would become impossible because sources would dry up (which is part of Session's game plan). The leaking is also a direct result of worried White House staffers, worried about the destruction around them. Action --> reaction, less worries --> less leaking.
BTW, I'm still wondering whether the information that Trump leaked to the Russian visitors (no WH staff nor photographer around to leak what really happened), was properly declassified before being shared. The Israelian secret services are still not pleased about him compromising their assets. While a President
can disclose such information, he/she can only do so
after formally declassifying it, not before, according to my information.
Cheers,
Bart