The 1958 NJ-13th Congresional Democratic Primary, the last time an incumbent Congressman lost a primary in NJ, four term Congressman Alfred Sieminski lost the backing of John V. Kenny's Hudson County political machine, instead being replaced with the winner Cornelious Gallager, his former Resident Secretary.
After Succeeding the first female congresswoman in the East—Mary T. Norton—in 1950, Siemski won three terms before nearly being toppled in 1956 in an election republican candidate (Norman Roth) believed was stolen from him after he lost by 57 votes
Alongside this loss, the Second place finisher was an independent Democrat, ally of fellow Jersey City Commissioner Mayor Charles S. Witkowski, 1949 Victory Ticket winner, Former Hudson senator, and son of Longtime Frank Hague Adversary James F. Murray Sr, Commissioner James F. Murray Jr
The independent Democrats had rode a reform movement to capter Jersey City Hall in 1957, electing reform Democrats to control the municipality.
However this defeat, along with their whole ticket losing the primaries marked a major loss to the reformist forces opposing John V. Kenny, who would rule Hudson until his indictment in the 1970s.
Should note that after this two other Congressmen would lose Reelection in primaries as Redistricting casualties, Cornelius Gallagher (NJ-13) himself and Steve Rothman (NJ-09)