INDIANOLA — Vermont Senator Bernie Sanders opened his first Iowa campaign event of the weekend with a unity message.“Certainly I hope that we are going to win, but if we do not win, we will support the winner and I know that every other candidate will do the same,” Sanders said. “We are united in understanding that we must defeat Donald Trump.”On Friday evening, a congresswoman who has been campaigning for Sanders booed Hillary Clinton from the stage of an event in central Iowa. The congresswoman issued an apology via Tweet on Saturday, but the episode — along with Clinton’s comments about Sanders in a documentary — highlighted the Sanders-Clinton conflict of 2016.Sanders at Simpson College event Saturdaybefore the Iowa Caucuses.Sanders has been off the Iowa campaign trail due to the impeachment trial. During a speech early Saturday afternoon in Indianola, he suggested the issues raised during the trial will be decided by voters in 2020.“Do we have an administration that thinks they are above the law, they can do whatever they want, they can lie, they can obstruct congress, prevent oversight?” Sanders asked.Many in Saturday afternoon’s crowd were Sanders campaign volunteers from other states who’re knocking on doors, hoping to persuade more Iowans to participate in Monday night’s Caucuses. According to Sanders, he’ll lose if turn-out is low.“Let us see Iowa having the largest Caucus turnout in the history of this great state,” Sanders said, to cheers as Sanders ended his remarks.In the 2016 Iowa Caucuses, Sanders finished three-tenths of a percent behind Clinton in the delegate count. Recent polls have suggested Sanders is leading or near the front of the competitors for the Democratic Party’s 2020 presidential nomination.