According to Evangelicals, before the Reformation, who were Christians if “Catholics are not Christians”? Every now and then I hear non-Catholic Christians, usually Evangelicals, say things along the lines of “Catholics are not Christians” or “the Catholic Church does not teach the true gospel.” Unless I am mistaken, Catholicism and various Orthodox churches were virtually the only Christian “denominations” that existed before the Protestant Reformation, aside from a heretical sect here and there (e.g., the Cathars). 

So for those who think the Catholic Church has abandoned the true faith or gospel, do they identify anyone from the time period of the fourth century A.D. until the Protestant reformation who had retained the true gospel?
Evangelicals would say that there were faithful churches who kept the gospel before the reformation. I think there are two historical factors involved:


Protestants recognise several movements of like-minded people before the reformation, such as the Lollards and Hussites. I think that Luther himself at one time admitted that his own beliefs essentially were Hussite. These movements did not have a strong lasting influence however. What gave Luther's movement longevity was a combination of the political situation and the printing press, which allowed his teachings to spread widely. It was not like all the precursors were condemned by the church either. Local disagreements and debates, especially by academics like Luther, were common. But printing took the debate to the continental level and demanded a response from the very top.
The Catholic Counter-reformation pinned down Catholic doctrine at the Council of Trent, removing a lot of flexibility from within the church. Several doctrines that would be denied at the council were permitted before, even if they would not have been explicitly endorsed. The Tridentine Catholic Church is different from the pre-reformation church, so that if Protestants say that the Catholic Church today is not truly Christian they are not implying that the pre-reformation Church was too.