The heated presidential election campaign is increasing tension in high school classrooms across Colorado, where students are asking civic teachers a simple question they can’t ethically answer: Whom do you support? There are students who fear they will be bullied or ridiculed by classmates for their political beliefs, but teachers say they work hard to promote debate, free expression and respect for other views. Maintaining classroom civility can be a tall order during any election, but this year’s particularly uncivil contest — with accusations of groping, lying and vote stealing — offers a special challenge. “In terms of my role, I’m just trying to give them answers and try to reassure them this isn’t a normal election,” said Daniel Niedringhaus, who teaches a “Politics & Problems” class of seniors at Boulder’s Fairview High School.