The American people are slow to wrath, but when their wrath is once kindled it burns like a consuming flame.
 Theodore Roosevelt, State of the Union Address. copy citation

Context

“This great country will not fall into anarchy, and if anarchists should ever become a serious menace to its institutions, they would not merely be stamped out, but would involve in their own ruin every active or passive sympathizer with their doctrines. The American people are slow to wrath, but when their wrath is once kindled it burns like a consuming flame. During the last five years business confidence has been restored, and the nation is to be congratulated because of its present abounding prosperity. Such prosperity can never be created by law alone, although it is easy enough to destroy it by mischievous laws.” source