Bonhoeffer yes but what what was Niemöller's position regarding the Nazis in 1932 and 1933?
If the Protestants formed a strong front against the Nazis, why was it necessary to form the Confessing Church?
Without getting into Bismarck's Kulturkampf, nationalist politics, patriotism, the aftermath of WWI, historic anti-Semitism, the völkisch movement and a fear of the Red Terror, the basic problems of the Church resisting Nazism was the deep split between Protestants and Catholics.
Hitler had a more difficult time with the Catholic Church because it is more monolithic and trans-national in leadership whereas Protestants are inherently fragmented and local in leadership. The Nazis could more easily remove, flip, or replace Protestant pastors than Catholic clergy. Additional problems were presented by the split between mainstream denominations and groups such as Jehovahs Witnesses and Seventh Day Adventists.
An additional problem preventing a united front against Nazism was that neither Jew nor Christian recognized that to the neopagan Nazis, Christianity was seen as just a large Jewish sect.
Niemoller did not oppose Hitler's accession to power, but I expect you knew that. However, eight years in Sachsenhausen and Dachau might indicate that he paid for that sin of commission, and his instigation of what became known as the Stuttgarter Schuldbekenntnis after the war indicated his true conversion.
The point of my post was not to compare Catholic to Protestant per se, but was, however, to note that German Protestants did play an active role against Hitler and some did so in high-profile ways.
"Through us infinite wrong was brought over many peoples and countries. That which we often testified to in our communities, we express now in the name of the whole church: We did fight for long years in the name of Jesus Christ against the mentality that found its awful expression in the National Socialist regime of violence; but we accuse ourselves for not standing to our beliefs more courageously, for not praying more faithfully, for not believing more joyously, and for not loving more ardently." -- Stuttgart Declaration of Guilt, 1945
And this from a man who spent eight years in concentration camps.