NEW YORK—CNN is canceling John King's evening news show, making him the first victim of the network's bad stretch in the ratings.

"JK USA" has aired at 6 p.m. ET since 2010. CNN said Wednesday that Wolf Blitzer's "Situation Room" would expand to three hours, and King will become the network's lead national campaign correspondent.

CNN has been suffering this spring in the ratings, particularly since interest in following the presidential campaign on television hasn't heated up. King's show was routinely CNN's least-watched in the evening.

King has covered seven presidential campaigns, four of them with CNN.