By early spring, California Governor Ronald Reagan, the leader of the Republican Party's conservative wing, had become Nixon's chief rival. In the Nebraska primary on May 14, Nixon won with 70% of the vote to 21% for Reagan and 5% for Rockefeller. While this was a wide margin for Nixon, Reagan remained Nixon's leading challenger. Nixon won the next primary of importance, Oregon, on May 15 with 65% of the vote, and won all the following primaries except for California (June 4), where only Reagan appeared on the ballot. Reagan's victory in California gave him a plurality of the nationwide primary vote, but his poor showing in most other state primaries left him far behind Nixon in the delegate count.