Something really strange happened in Tennessee last week. Democrats elected a fright-wing conspiracy theorist named Mark Clayton to be their U.S. Senate candidate—and the state party promptly disavowed him.

It’s fair to say that if this were a Republican Senate nominee, there would be wide public outcry. Instead, there’s just awkward silence.

Clayton is a fringe figure, someone whose beliefs span talk about the new world order, an alleged NAFTA superhighway, and FEMA prison camps. He also is vice president of an organization that calls itself Public Advocate of the United States, which pushes an extreme social-conservative agenda with such a negative obsession with gay rights that the Southern Poverty Law Center has designated it a hate group. Clayton’s political self-brand isn’t exactly making a broad comeback within the southern Democratic Party. So how did this happen?

First, the practical considerations. The Tennessee Democratic Party has been taking a beating in recent years. It holds just two of nine congressional seats, and the rigged system of redistricting promises to make that margin worse. The governorship, the state legislature, and both U.S. Senate seats are all held by Republicans. Incumbent Sen. Bob Corker, who narrowly won his Senate seat running against Harold Ford Jr. in 2006, has accumulated an intimidating multimillion-dollar war chest and a decent overall record. These dynamics meant that no credible, well-funded Democrat decided to get in the race in 2012. One additional benefit for fringe candidates—it takes only 25 signatures to get on the ballot.

Clayton’s 20-point primary victory seems to be accountable to his last name. “The guy hasn’t even updated his website since 2008,” Sean Braisted of the Tennessee Democratic Party told me. “So the only logical thing is that he was the first name on the ballot.”

This is the same lame dynamic that led Alvin Greene to be South Carolina Democrats’ nominee against Sen. Jim DeMint in 2010. That particular spectacle was amusing, and occasionally entertaining, but it was essentially depressing for at least two reasons. First, because if voters really do pull the lever for the first name they see in such large numbers, it doesn’t speak well of our democracy—we look dumb. Second, citizens in the state have been denied a credible general-election contest.

There is an overall cautionary tale with ramifications beyond Tennessee: this is what can happen in one-party states. The ideological polarization of the two parties means that there are fewer and fewer conservative Democrats or progressive Republicans. That, in turn, means that there are fewer Southern Democrats who can win statewide and Northeast and Pacific coast Republicans. Potentially credible candidates—like the Democratic mayors of Tennessee’s four largest cities—decide that it is not worth being a sacrificial lamb in the face of a presidential landslide. Add a low-turnout primary, and fringe candidates can get their 15 minutes of fame.

But the result is an embarrassment to Tennessee and a state party that once put forward significant national figures from Andrew Jackson to Estes Kefauver to Al Gore. Six years ago Ford came within 2 1/2 points of his own enduring national career. That space is now being filled by a joke of a candidate, but no one is laughing. Well, Corker might be—he’ll have the luxury of winning a second term to the U.S. Senate without campaigning.

Serving in the U.S. Senate is an honor, a serious job—and it deserves serious candidates, no matter how uphill the race is for a party that’s fallen out of favor. More important, the voters of the state deserve a real choice when they go to the ballot booth.