The Impressionists were radicals--not necessarily on the political left, but radicals in that they were trying to change the core of how art was made, exhibited and marketed. In this, and in their commitment to modern life, the Impressionists capitalized on the innovations and ideas of the painters Gustave Courbet and Édouard Manet and on the poet/critic Charles Baudelaire.
Gustave Courbet. Portrait of Charles Baudelaire, 1849. Fabre Museum.
Édouard Manet, Music in the Tuileries, 1862. National Gallery of London.