Zerban had hoped his campaign would benefit from the heightened scrutiny Ryan was under as a national candidate, but that never happened.
"We knew this was a tough race getting in," Zerban said, adding that it was too early to say whether he'd challenge Ryan again in two years.
The 1st District stretches from the shores of Lake Michigan through industrial zones, bedroom communities and farm fields until it reaches Ryan's hometown of Janesville to the west. The seat, which also includes some south Milwaukee suburbs, has been in Republican hands since 1995.
State law allowed Ryan, a 42-year-old married father of three, to run for Congress and vice president at the same time.
If he had won both races, Ryan would have had to resign from Congress. A special election would have been held to fill the House seat.
Dinesh Ramde can be reached at dramde(at)ap.org.