Great catch here by Tim Murphy. Democrats in Tennessee, who didn't really try to recruit an opponent to Sen. Bob Corker, ended up nominating a guy with a bland name who appeared at the top of the ballot and ran in the same primary four years ago.
He's also a conspiracy theorist.
On his issues page, [Mark] Clayton sounds more like a member of the John Birch Society than a rank-and-file Democrat. He says he's against national ID cards, the North American Union, and the "NAFTA superhighway," a nonexistent proposal that's become a rallying cry in the far-right fever swamps. Elsewhere, he warns of an encroaching "godless new world order" and suggests that Americans who speak out against government policies could some day be placed in "a bone-crushing prison camp similar to the one Alexander Solzhenitsyn was sent or to one of FEMA's prison camps." (There are no FEMA prison camps.)
The Clayton campaign site is down, but you can still read his various opinions on webarchive's cache. You can read about his concernsm like how "the neo-conservative side of the Republican party... has a known reputation for sharing power and being 'in bed with' the homosexual Log Cabin Republican group." And you can see the only video evidence of his campaign.
How does someone like this win? He's running as a Democrat in the South. The "kook nobody actually wanted" phenomenon is now a biennial tradition. In 2008, a former Pat Buchananite named Bob Conley won the Democratic nomination to oppose Sen. Lindsey Graham in South Carolina. In 2010, more famously, an unemployed man named Alvin Greene won a landslide victory in the same state, becoming the Democratic opponent to Sen. Jim DeMint. As conservatives have hot-footed it out of the Democratic Party in these states, well-organized kooks -- or, hell, people with normal-sounding names -- have been able to win nominations. Democrats thought that they'd hit rock bottom in Texas two years ago, when a Lyndon LaRouche cultist named Kesha Rogers won the nomination in the old Sugerland-centered Tom DeLay seat. Rogers's platform of space exploration and Obama impeachment got national attention -- negative national attention. And guess who won the nomination for this seat in 2012? Kesha Rogers.