a.k.a. Mr. Republican
The very epitome of cryptofascism, Buchanan is a noted paleoconservative and racist, suspected holocaust denialist (discussed here, with links. Alternatively, the Holocaust was France and Britain's fault), Nazi sympathizer and believer in the Zionist Conspiracy. A good sample of his views, in his own words, can be found here.
Buchanan needs little introduction, I guess, but anyway: He was originally a senior adviser to presidents Nixon, Ford, and Reagan, and an original host on CNN's Crossfire. He sought the Republican presidential nomination in 1992 (where his speech during the Republican party nomination might have scared several moderate Republicans to vote for Clinton – invented the concept of ”culture wars”) and again in 1996. He ran on the Reform Party ticket in the 2000 presidential election.
He co-founded The American Conservative magazine and launched a foundation named The American Cause, has been published in Human Events, National Review, The Nation and Rolling Stone. Currently Buchanan is a political commentator on the MSNBC cable network including the show Morning Joe and a regular on The McLaughlin Group.
He is most noted today for his opposition to free trade and immigration, both legal and illegal. He could be considered an "economic nationalist", but is more likely simply a xenophobe. He is (by the same token) a staunch opponent of military actions related to the war on terror. He is, however, very positive to using torture on people suspected of terrorism.
Also an amateur historian; in ”Churchill, Hitler and the Unnecessary War” he takes a pro-German view of World Wars I and II. Buchanan argues that the US shouldn't have gotten involved in World War II, that Churchill helped provoke Japan to attack Pearl Harbor, and that Hitler could have been contained. Curiously, he rejects evolution because, among other things, it lead to Hitler (no, these people aren’t overly concerned about distinguishing the question of the truth of a claim and consequences of believing a claim, presumably because they aren’t overly concerned with truth to begin with); discussed here and here.
Diagnosis: Insane crackpot and zealot, evil. Relatively influential though his impact is probably smaller than his media exposure could be taken to indicate.