“In a climate of so much mistrust in government, I think it is important for people who want to be in a position of leadership to show as much information about themselves as possible,” Robertson said.

Although individual income tax returns are private, most U.S. presidential candidates dating to the early 1970s have chosen to release their returns.

In some states it also is common for governor candidates and other statewide officials to make their returns available for scrutiny.

In Illinois, for example, voters learned in 2015 that Gov. Bruce Rauner, a wealthy investor, earned $58 million the previous year. Farther down the ballot, former Illinois Lt. Gov. Sheila Simon released her tax returns in her unsuccessful bid for comptroller.

Gov. Jay Nixon, who is leaving in January after two terms as chief executive, has not typically released his returns.

The Post-Dispatch also has requested the tax returns for the candidates running for U.S. Senate, incumbent Republican Roy Blunt and Democratic challenger Jason Kander.