CEDAR RAPIDS — The White House has rejected House Democrats’ demand that President Donald Trump turn over his tax returns, but Sen. Joni Ernst thinks the president should voluntarily release them.“I think he should voluntarily release them. Yes,” she said Wednesday during a conference call with Iowa reporters.Treasury Secretary Steven Mnuchin earlier this week told majority House Democrats that he would not furnish the president’s tax returns despite a 1924 law that seems to explicitly give Congress power to request those documents.