Evangelical Protestants have been suspicious of the Latter-Day Saints since the church began. Until recently, even well-known ministries described Mormonism as a cult.
However, evangelical Protestants are also the core constituency of the Republican Party today. So, when the G.O.P. nominated a Mormon for president, some thought evangelicals would be cool to Mitt Romney, a Mormon bishop and very active church leader.
Instead, evangelical Protestants dropped their opposition to Mormonism.
Though Mitt Romney did not win, I think his candidacy normalized Mormonism in American politics as much as John F. Kennedy's candidacy normalized Roman Catholicism in American politics.