DES MOINES — Staff for three U.S. Senators running for president scrambled to arrange campaign events around the state this weekend during a brief break in the senate’s impeachment trial. Vermont Senator Bernie Sanders told a crowd in Sioux City last night he had planned to spend this week campaigning here.“I can’t do that now because I’ve got a constitutional responsibility,” Sanders said, “and unlike the president of the United States, I actually believe in the constitution.”Sanders said he has “zero idea” what the impeachment trial’s schedule may be this week — or how long it may go in February.Massachusetts Senator Elizabeth Warren had to cancel an event in Burlington because of the impeachment trial’s Saturday morning session, but added one in Davenport Saturday night. Warren spent the weekend traveling through eastern Iowa and met with a group of volunteer leaders in Cedar Rapids before flying back to Washington.“I’m there for the trial and I will be there for the trial, but it’s very hard not to be here in Iowa” Warren told Radio Iowa Sunday morning. “I’m very grateful that so many people have volunteered, have engaged, have said: ‘We know you’re in Washington, so we’ll get out there.’”Minnesota Senator Amy Klobuchar is boarding a 6 a.m. flight to D.C. this morning.“It is with some bitter sweet sentiments ’cause I know I’m going back to do good,” Klobuchar told Radio Iowa Sunday evening, “but I would love to be here.”Klobuchar said she had intended to make another 99-county tour this month, after completing one at the end of December. Klobuchar suggests there’s now more pressure on Republican senators to call former National Security director John Bolton as a witness in the impeachment trial. On Sunday night, The New York Times reported Bolton’s book draft alleges President Trump wanted to freeze aid to Ukraine until the country investigated Joe Biden and other Democrats.“With Mr. Bolton saying that exactly what we said happened — happened, for them to deny him testifying would be wrong,” Klobuchar said, “so that’s what I’m going back to work on.”Former Vice President Joe Biden told an audience in Ankeny he expects to be a focus of Trump’s impeachment defense, but Biden suggested it will not be an issue for Iowa Caucus-goers as they make their decision next Monday night.“I’m not sure it will because so far it hasn’t,” Biden told Radio Iowa Saturday evening. “I mean, they’ve beaten the living hell out of me and my numbers have gone up, not down.”Former South Bend Mayor Pete Buttigieg appeared at a town hall hosted by Fox News last night and the first audience question was whether Trump should be removed from office.“If he’s not, it’s going to send a message that this Senate, or at least Senate Republicans today think that it’s okay to cheat, it’s okay to involve a foreign government or pressure a foreign government to get involved in American elections,” Buttigieg said.Buttigieg said the American people will have the last word, at the ballot box.