On December 20, 2018, the Senate Ethics Committee voted unanimously to dismiss a complaint against Boulton related to sexual misconduct allegations. The committee ruled that they did not have jurisdiction in the matter because the alleged misconduct took place prior to Boulton's election. Jerry Behn (R), the committee chair, said that the committee did not attempt to determine whether the allegation was valid. The Des Moines Register reported that three women accused Boulton of inappropriate touching on May 24, 2018. Boulton said in a statement, "It is devastating to me that anything that I said or did crossed that line because I know me, and I didn’t do that in any sort of intentional way, and if I misread a situation, I apologize for it. But it doesn’t matter. I’m not trying to make excuses, I’m not trying to change anyone’s account. All I’m here to say is I’m sorry, I apologize and I understand." His wife said she supported her husband "100 percent without a doubt." In response, Senate Democratic Leader Janet Petersen said that sexual harassment was unacceptable and indicated she would support an investigation into the allegations against Boulton. On December 7, Petersen announced that she would not appoint Boulton to any committees for the 2019 legislative session pending the Ethics Committee investigation.

See also: Sexual assault and harassment in American politics (2017-2018) Nate Boulton was mentioned during a wave of sexual assault and misconduct allegations in 2017 and 2018. On May 24, 2018, state Sen. Nate Boulton, a Democratic candidate for Iowa governor, suspended his campaign after being accused of sexual misconduct. On May 21, 2018, the Des Moines Register reported that three women accused Boulton of inappropriate touching. Boulton said in a statement, "It is devastating to me that anything that I said or did crossed that line because I know me, and I didn’t do that in any sort of intentional way, and if I misread a situation, I apologize for it. But it doesn’t matter. I’m not trying to make excuses, I’m not trying to change anyone’s account. All I’m here to say is I’m sorry, I apologize and I understand." His wife said she supported her husband "100 percent without a doubt." Boulton's Senate colleagues called for his resignation from the Iowa State Senate. Senate Democratic Leader Janet Petersen said sexual harassment was unacceptable and indicated she would support an investigation into the allegations against Boulton if he did not resign. On December 7, Petersen refrained from appointing Boulton to any committees for the 2019 legislative session. Petersen said, "I will defer making any committee assignments for Senator Boulton until the Senate Ethics Committee completes its ongoing investigation into the complaint filed against him."