My favorite excerpt from Aida D. Donald's biography of Theodore Roosevelt Lion in the White House (2007):
"Roosevelt was the only progressive president in the history of the Republican Party. In fact, Roosevelt's presidency was one of the great forward, or progressive, eras in the nation's history as a whole. His party never again reached such heights in advanced legislation or in the care of the people. No Republican president since has embraced the idea of creating, through active government, the greatest good for the greatest number of people."