A "bellwether," quite literally, is a male sheep wearing a bell that leads the flock - or at least allows a farmer to find his sheep, because the clanging ram is never too far from the rest of the group.
For most of a century, Missouri has been the nation's bellwether. Every four years, a majority of voters in the state in the center of the country - a near perfect mirror of its demographics, geography, economics and politics - predictably cast their ballots for the candidates the nation as a whole chooses to win the White House.
That changed in 2008, when Missouri voters went for Republican John McCain by a razor thin margin over Democrat Barack Obama. It was just the second time in a century that Missouri didn't side with the winning presidential candidate.
Should Republican Rep. Todd Akin - who offended millions of Americans with insensitive remarks about rape and pregnancy - rebound this November to defeat Democratic Sen. Claire McCaskill, Missouri will probably need to turn in its bell for good.
Obama has more or less conceded the state to presumptive Republican presidential nominee Mitt Romney. Should Akin manage to beat McCaskill without the support of Romney or other top Republicans, including all five living current or former GOP senators from the state, voters will solidify that an already red-leaning Missouri has truly become a rock-ribbed Republican stronghold.
"There is too much at stake here in this election," Akin implored in an online fundraising plea sent heading into the weekend. "Today, let's show Claire once and for all that Missouri is going Republican Red this November."
To be sure, Missouri has been trending Republican for several years. The state Legislature, which swung to the GOP a decade ago, now has one of its largest Republican majorities in state history. And in 2010, Missourians ousted Democratic Rep. Ike Skelton from a seat he held for 34 years in favor of a Republican who had been the spokeswoman for a successful ballot campaign to engrave a gay-marriage ban in the state constitution.
Obama has made no campaign appearances and run no TV ads in the state. Yet political scientists have been reluctant to lump Missouri in the same reliably Republican category as neighboring Kansas or many of its new peers in the Southeastern Conference, where the University of Missouri now plays its sports.
"It's pretty obvious that it's trended a little bit red," said Dave Robertson, a political science professor at the University of Missouri-St. Louis. "An Akin victory in November would be a very, very strong indicator that this state is comfortably red."
Missouri has a long history of divided loyalties - its residents fought for both the Union and Confederate armies during the Civil War. That division has historically made Missouri a microcosm of the nation.
Geographically, Missouri has large cities on its east and west "coasts," with a rapidly growing population in the south and a largely rural, agricultural base in the center - just like U.S.
Demographically, the racial composition of Missouri's residents, their average age, marital status and educational background all have historically been fairly close to national norms. And although the median household income has slightly trailed the nation, so has Missouri's cost of living - making its poverty rate on par with that of the rest of the country.
That has begun to change. Most notably, the 2010 census revealed that Missouri's racial mix no longer is roughly the same as the national average. More of its residents are white (83 percent compared with 72 percent nationally) and significantly fewer Missourians are Hispanic (3.5 percent compared with more than 16 percent nationally). A far greater percentage of Missouri households speak English only than do nationally, which perhaps explains why state voters adopted a 2008 constitutional amendment making English the official language for government proceedings by an overwhelming 86 percent.
Democrats still can win statewide elections in Missouri, but they typically do so by positioning themselves in the political center. Democratic Gov. Jay Nixon, for example, has campaigned on a Republican-like theme highlighting his tax cuts and spending cuts while running commercials that describe him as "independent."
McCaskill cast herself as a moderate and portrayed Akin as an extremist even before Akin's gaffe a week ago in which he told a St. Louis TV interviewer that women's bodies have ways of avoiding pregnancy in cases of "legitimate rate." Akin has since apologized and said he was wrong.
A poll released Saturday by the St. Louis Post-Dispatch and TV station KMOV showed McCaskill with 50 percent support, compared with 41 percent for Akin. The telephone poll of 625 registered Missouri voters who said they were likely to vote in the November election was conducted Wednesday and Thursday. It had a margin of error of plus or minus 4 percentage points.
Republican Judy Loman, 68, of the rural central Missouri town of Versailles, said she believes Akin's apology is sincere although she acknowledged "mixed feelings" about whether to vote for him in November. Regardless, Loman said, she would not vote for McCaskill.
In the primary, Carolyn Hinze supported one of Akin's rivals and she didn't like Akin's recent remarks about rape. Yet the 71-year-old retired insurance agent from Joplin plans to remain a loyal Republican and vote for Akin in November.
"He's a little more conservative than I am, but I don't think he's dangerous," Hinze said.
Rick Althaus, a political science professor at Southeast Missouri State University, said that no matter the outcome of the Senate race, he's already changed the textbooks at his school. For more than a decade, the book used for the introductory course on American government included a section about Missouri politics written by Althaus that explained the state's bellwether nature. He removed that description for the 2012 edition.
Simply put: "Missouri is losing its bellwether status," Althaus said.