WASHINGTON -- Flip, flop. Flip, flop.
No, that's not the sound of a politician switching positions on a hot-button issue.
It's the sound of Missouri voters switching from Republican to Democrat - and back again, and again - when deciding who to elect for the Show-Me State's much-coveted U.S. Senate seat now up for grabs.
"There's been no stability here," Kenneth Warren, a political science professor at St. Louis University, said in reference to the seat that Democrat Claire McCaskill now holds. "It's been more susceptible to the political climate of the time."
That helps explain why - almost two months after Republican Todd Akin sparked a national controversy with his comments about "legitimate rape" - the GOP Senate nominee remains within striking distance of McCaskill. Two polls released last week showed McCaskill up by 6 percentage points, within the margin of error of about plus or minus 4 percentage points.
After Akin's remarks - in which he said that women who are victims of "legitimate rape" rarely get pregnant because the female body can somehow prevent that from happening - election handicappers in Washington decided that his chances of winning were essentially zip. National GOP strategists similarly concluded that spending money is Missouri would be a waste of precious resources.
In another swing state, say Ohio or Virginia, Akin probably would be toast.
But in Missouri, observers point to the state's rich history of nail-biter elections and its evenly divided political landscape as evidence that this race is not over. While many political observers in the state give the edge to McCaskill, no one thinks it will be a blowout.
"This race will be (decided by) less than five percentage points," predicted Andrew Blunt, who ran the successful U.S. Senate campaign of his father, Roy Blunt, in 2010.
Roy Temple, a consultant and former executive director of the Missouri Democratic Party, agreed that the contest is still fluid.
"It's 30 days out, and we've seen weirder turns than this," Temple said.
Without question, Missouri has seen more than its fair share of topsy-turvy cliff-hangers. This Senate seat in particular has changed party control three times in the last three elections.
The volatility seemed to first set in with the election of Republican John Ashcroft, who won the seat in 1994 after then-GOP Sen. John Danforth retired. Ashcroft was both a popular and polarizing figure. He once proudly defended his conservative credentials by saying there were only two things you could find in the middle of the road - "a moderate and a dead skunk" - and he didn't want to be either.
His 2000 re-election bid against then-Gov. Mel Carnahan was a clash of titans - both were well-known and raised gobs of money. Three weeks before the election, with polls showing a dead heat, Carnahan was killed in a plane crash. It was too late to take his name off the ballot, and amid an outpouring of grief and sympathy for the Carnahan family, the governor was elected posthumously.
That bizarre outcome - with Carnahan's wife Jean being appointed to fill her late husband's seat - guaranteed that Missourians would have go to the polls again in two years to pick a candidate for this Senate seat - an election that wouldn't have happened if not for the plane crash.
With only two years under her belt, Carnahan was ousted by Republican Jim Talent in 2002. Talent served out the remaining four years of that term, before being defeated in 2006 by McCaskill.
J. Brad Coker, a pollster who has been taking the political pulse of Show-Me State since the 1980s, said the repeated flips from Republican to Democratic control reflect Missouri's status as a microcosm of the country - almost evenly divided between the two parties and subject to broader political winds sweeping the electoral landscape.
"This seat has ebbed and flowed with the (national) party tide, and it's always been close," said Coker.
He and others noted, for example, that Talent beat Carnahan, by 49.8 percent to 48.7 percent, in what was a great political year for Republicans across the board. And McCaskill beat Talent, 49.6 percent to 47.3 percent, in what was a wave election for Democrats.
And until Akin's rape-and-pregnancy comments, Republicans seemed poised to snatch the seat back from Democrats in what looked, early on in this election cycle, as a tough year for Democrats nationally.
McCaskill appeared particularly vulnerable because Missouri has tilted more toward the GOP in recent years. Obama lost the state by 3,903 votes in 2008, even as he racked up big wins in other parts of the country. And Blunt easily defeated Secretary of State Robin Carnahan in 2010, another good GOP year nationally.
"There's been some partisan shift in the state" toward Republicans, said Temple.
Some of that is due to demographic changes, with places like Southwest Missouri, a conservative bastion, seeing a spike in population, while the Democratic stronghold of St. Louis has experienced a continued population decline. Experts also say the issues in this election - a sour economy and the spiraling debt - favor Republicans right now, partly because the incumbent president is a Democrat and is being held accountable for those negatives.
With President Obama not very popular in Missouri, said Temple, "you have a voluble, combustible mix."
In addition to that backdrop, McCaskill has her own problems - starting with approval ratings under 50 percent mark.
Warren said some liberal Democrats in the state are still angry about McCaskill's decision to mount a primary challenge to former Gov. Bob Holden. She beat Holden but lost the general election, leaving many in her party bitter.
Meanwhile, some conservative Democrats and independents see McCaskill as too closely allied with Obama. Although she has worked to compile a centrist voting record and tried to cultivate a maverick imagine in her first term, many voters feel like she sold them a "bill of goods," as Coker put it.
"She was elected the first time based on (a campaign promise that) 'I'm going to be an independent voice,' " said Coker. "Then Obama comes along two years later, and she fully embraces him in the campaign and suddenly starts voting for high-profile items on his agenda, such as the 2009 stimulus package and the health care reform law.
McCaskill's supporters say that's a bad rap - that while she is friends with Obama, she has split with him on key issues, such as the Keystone Pipeline and coal regulations. She's been "very pragmatic" and "in the center," said Democratic Rep. Russ Carnahan, Jean Carnahan's son.
And Akin, he said, "has given up so many errors it's really changed the dynamic of the race."
Still, asked about McCaskill's prospects, Carnahan said the vote will be "split down the middle." And he offered up a little Missouri political trivia: the last Democratic senator to win re-election in the state was Tom Eagleton, in 1980.