The people may change, but not the political parties. For the most part, that's the backdrop for this year's Missouri Senate contests.

Statewide, half of the Senate's 34 seats are on this year's ballots. But most of those seats have largely become locks for one party or the other. As a result, there's little chance this year that Missouri Democrats will make much of a dent in their minority status, or that the GOP will add much to its already considerable majority.

Republicans control 23 -- or 67.6 percent -- of the chamber's 34 seats. Democrats hold only 11 seats, their smallest share of the Senate in more than 60 years.

But the polarization in many of those districts also means that Tuesday's primary elections are key. In many cases, the victor in the region's contested party primaries for the state Senate will have no serious opposition in November.

The region has four major Senate primary fights -- two involving Democrats (Districts 14 and 24) and two with Republicans (Districts 2 and 26). Only one, the 24th, is seen as a true swing district.

Here's a snap shot of the candidates and the issues in each of the four:

DISTRICT 2

As state Rep. Cynthia Davis sees it, Sen. Scott Rupp, R-Wentzville, is simply not a true conservative. So Davis, R-O'Fallon, is challenging Rupp's bid for re-election in the GOP-leaning district.

Rupp sees Davis as a self-promoter whose record in the House doesn't come close to matching his.

Rupp, 36, is a banker on good political terms with many of the state's top Republicans. His campaign has raised and spent about four times as much as Davis.

Scott Rupp and Cynthia Davis

Davis, 50, is the mother of seven children, co-owner (with her husband) of a Christian bookstore and somewhat of a political renegade.

Davis has attracted national attention over such efforts as her bill to make it more difficult for Missourians to divorce , her avid opposition to abortion and her 2009 criticism of federal summer food programs for low-income children. Davis asserted that "hunger can be a positive motivator."

Rupp cites his roles in passing the 2008 law that gives the Missouri Highway Patrol the power to check the residency status of anyone headed for jail, in helping to craft state budgets during tight economic times and in getting Proposition C -- which seeks to block enactment in Missouri of the new federal health-care mandates -- through the state Senate and onto Tuesday's ballot.

Rupp also disputes Davis' assertion that he hasn't been active enough against abortion. Missouri Right to Life, the state's largest anti-abortion group, has endorsed Davis.

Both also are tangling over guns. The National Rifle Association has endorsed Rupp's re-election, but it also has given Davis its top "A" rating. Her latest campaign flier asserts that she's the only candidate with a concealed-weapon permit.

Davis ran into trouble with the Missouri Ethics Commission a few years ago, and paid a fine, after the state Democratic Party filed a formal complaint alleging that that she improperly used campaign money for personal expenses. Another similiar complaint recently was filed against Davis, who contends the newest case is politically motivated.

Her campaign says it has, in turn, filed ethics complaints against Rupp. He says he has yet to be notified by the Ethics Commission that any complaints have been filed, which Rupp asserts is a signal that Davis' alleged action was motivated by politics, not facts.

DISTRICT 14

Four Democrats -- three of them legislators and one a former mayor -- are battling over the post being vacated by state Sen. Rita Days, D-Bel Nor, who must retire because of term limits. Because no other party is fielding a candidate, the Democrat who wins Tuesday is guaranteed to get the seat. Days had remained neutral but came out Thursday in favor of state Rep. Maria Chappelle-Nadal.

State Rep. Ted Hoskins, D-Berkeley, is a businessman and former mayor of Berkeley who is completing the last of four terms in the Missouri House. He has won praise and criticism over his amiable ties with House Republicans, who've controlled the chamber since 2003. In 2009, he was the only Democrat named to head a House committee.

Clockwise from upper left: Ted Hoskins, Maria Chappelle-Nadal, Joe Adams, Don Calloway

State Rep. Don Calloway, D-Bel Nor, is a lawyer and just completing his first term in the state House . Over the past year, he's attracted a lot of attention over his opposition to the embattled leadership running the Northeast Ambulance and Fire Protection District. Calloway has joined in a successful legal fight to challenge the finances of the district.

Calloway and Hoskins each have received significant financial support -- $30,000 apiece -- from Progress for the Saint Louis Region, a new campaign committee that initially is being bankrolled by wealthy financier/philanthropist Rex Sinquefield. Both candidates have said they share Sinquefield's desire for more educational options for students who live in failing districts. That support also has touched off concern among Sinquefield's school-choice critics.

Chappelle-Nadal, D- University City, is completing her third term in the state House. Her first bid for office in 2004 caught the attention of then-presidential contender Howard Dean, who later named Chappelle-Nadal as one of Missouri's superdelegates to the 2008 Democratic presidential convention. She was chosen by the State Department last winter to travel to Iraq as part of a contingent of eight women elected officials to serve as election observers for Iraq's March 7 election.

Chappelle-Nadal angered some state Democratic leaders in 2008 when she participated in a robo-call to aid Republican Mike Gibbons, then running for Missouri attorney general. Chappelle-Nadal also has run afoul of the region's main gay-rights group , PROMO, over public disclosure of her Tweets referring to the sexual orientation of Terry Crow, a University City councilman who is gay and made an unsuccessful bid for mayor.

Former University Mayor Joe Adams has been touting his executive experience ever since he left office in the spring and launched his state Senate bid. Adams is a former president of the St. Louis County Municipal League and of the Missouri Municipal League.

He has been endorsed by state Sen. Joan Bray , D-University City, former state Sen. Wayne Goode, and the 14h District's Democratic township committeepeople. But Adams also has been less successful at raising campaign money than his rivals, in part because he has not attracted large donors like his Democratic rivals. Adams' allies say that's evidence that he will be more independent; his rivals disagree.

District 24

Former state Reps. Sam Page and Barbara Fraser have been locked in a Democratic battle for months for their party's nomination to succeed Bray, who must retire because of term limits.

Both are emphasizing their previous legislative experience and their political ties. Bray is backing Fraser , while Page has the support of U.S. Rep. William Lacy Clay , D-St. Louis. An earlier rival, state Rep. Mike Corcoran, has endorsed Page since dropping out.

Fraser is a former history teacher and former member of the University City School Board. After serving eight years in the state House, Fraser won election in 2006 to the St. Louis County Council. She currently is council president.

Sam Page and Barbara Fraser

Page is a physician who served on the Creve Coeur City Council before he was elected to the state House in 2002. In 2008, he was the Democratic nominee for lieutenant governor, losing to Republican incumbent Peter Kinder.

Both candidates emphasize their support for public education, making college affordable and the need for the state and the region to encourage economic growth. Both say they know how to work with Republicans.

Page also focuses on health care, saying, "I have led the charge to expand access."

Page cites his opposition to the Legislature's 2005 cuts to the state's Medicaid rolls and, since leaving the House, his support for the unsuccessful effort by Gov. Jay Nixon and the state's hospitals in 2009 to expand coverage by using larger fees by the hospitals to match more federal Medicaid dollars.

Fraser says her service in the House and the County Council "sets me apart" and give her stronger insight into the region's problems.

In the House, Fraser particularly focused on children's issues. On the council, she "led the way with the smoking ban'' that county voters approved overwhelmingly last year.

Although Page has raised more campaign money, the two have had similar budgets over the last six weeks of the campaign. And the tone of their contest has gotten more combative, with each challenging the other's effectiveness and energy.

Also in the Democratic primary is Helen Steele Burton, who has not actively campaigned.

The victor will face Republican John Lamping, a first-time candidate who has amassed a hefty war chest while he has watched the two Democrats fight it out.

DISTRICT 26

Arguably the region's highest-profile, and nastiest, state Senate fight has been among three Republicans duking it out to succeed state Sen. John Griesheimer, who like Bray and Days must retire because of term limits.

The three chief contenders -- state Rep. Brian Nieves, former state Rep. Jack Jackson and former Washington, Mo., mayor Richard Stratman -- are competing with campaign mailers, TV and radio ads. (Also in the race is Donald Meyer of Labadie, who not actively campaigned.)

Nieves and Jackson also admit campaigning on their regular radio shows.

The key issues: Who's the most conservative and who can be more effective?

Stratman has the backing of Griesheimer and some other major Republicans. Nieves is popular with the Tea Party crowd. Jackson, a veteran, has strong ties to veterans' groups.

From left: Richard Stratman, Brian Nieves, Jack Jackson

During the final week, Stratman's campaign is running robo-calls that feature his pregnant adult daughter, who emphasizes her father's opposition to abortion.

(Click here to view Stratman's TV ad.)

Stratman also has been attacking Nieves' record, accusing him of casting votes in favor of legislative pay raises. Nieves denies ever voting for House pay hikes, and has launched robo-calls that accuse Stratman of lying.

Stratman criticizes Nieves and other GOP legislators for using federal stimulus money to balance the state budget. He says the money should have been used for construction projects or given back to the federal government.

Jackson, meanwhile, has fired off statements this week highlighting his promise that, if elected, he'll call for state senators "to take a morals and ethics pledge."

"If you are always worried about someone finding skeletons in your closet then you can't be working as hard as you can to find ways to revive the economy and bring back good jobs." Jackson said. "My commitment to ethics also includes my strong refusal to use negative political tactics."

Meanwhile, 24th District residents and political activists are reporting the circulation and mailing of letters that make salacious accusations against Nieves. Stratman and Jackson deny any involvement or knowledge of the letters or their assertions.

On Tuesday, Nieves called the letters "last-minute, desperate moves'' by his opposition, and has decried such tactics on his daily radio show .