Congressman Tim Johnson has endorsed fellow Republican Congressman Don Manzullo in his primary bid against a freshman incumbent.

Manzullo faces Congressman Adam Kinzinger, an Air National Guard pilot elected in 2010.

Their primary battle in north-central Illinois is 1 of the most intense in Tuesday's primary election. A new congressional map drawn by Democrats put much of Kinzinger's old district into Manzullo's, forcing an incumbent runoff.

The new 16th District curves through north-central Illinois from the Wisconsin border to the Indiana state line.

In the endorsement, Johnson cites Manzullo's fiscal conservatism and family values.

Johnson is a longtime central Illinois congressman. He faces a primary challenger for the first time in a decade in his expanded district.

Kinzinger has been endorsed by GOP Congressman Aaron Schock.