Campaign flyers that promote a white candidate with racially charged language. A TV ad that includes video of mostly Latino or Black people who are homeless, fighting or engaged in crime. News stories that focus on the alleged mistreatment of legislative staff by a candidate who’s a Black woman — but don’t scrutinize other candidates’ reputations as bosses. All of these have fueled recent flashpoints over race and gender as a historically large, and notably diverse, field of candidates campaign to be Denver’s next mayor in the April 4 election. Disputes over campaign tactics have put two white candidates — Mike Johnston and Chris Hansen — on the defensive.