In the run-up to the US presidential election in 2004, frieze asked 22 artists to respond to four questions on the relationship between art and politics. With the build up to this year's presidential election in the United States, we asked a selection of artists, curators and writers to answer the same four questions: What constitutes political art? Has there been a resurgence of it? What is an example of art that is politically effective? Is political art preaching to the converted? For the first part of this series, the responses of Nato Thompson, Carolyn Christov-Bakargiev, Oliver Ressler and Helen Molesworth.