JOHNSTON, Iowa (AP) — Democrats vying to challenge Republican Sen. Charles Grassley in his upcoming re-election race have used a televised debate in Iowa to criticize the longtime senator’s involvement in a Supreme Court nomination fight.

The four candidates, including former Iowa Lt. Gov. Patty Judge and state Sen. Rob Hogg, used the hour-long debate Thursday night in Johnston to highlight Grassley’s decision not to hold hearings for President Barack Obama’s U.S. Supreme Court pick. The issue is seen by Democrats as an opening to seriously challenge Grassley in November.

The candidates, including attorney Tom Fiegen and former state legislator Bob Krause, were also asked about their plans to address issues ranging from water quality to the minimum wage.

The debate comes less than two weeks before Iowa’s June 7 primary.