PIERRE, S.D. (KELO) -- The Legislature's Republicans head into Tuesday's general election assured of keeping their House and Senate majorities. But there's great uncertainty about who the leaders will be -- and much of it ties back to challengers who knocked out incumbents during the Republican primaries in June, largely over the issue of a proposed carbon-dioxide pipeline. Lee Schoenbeck is retiring as the Senate president pro tem. For the past four years, he's been the one who's steered much of how the chamber has run, such as deciding who's assigned to which committees and where each piece of legislation gets sent for a mandatory hearing. Observers point to a handful of Senate contests as the key to which Republican faction will have more members after Tuesday and will then take the reins for the 2025-26 term. Insiders expect Chris Karr and Casey Crabtree will vie to succeed the 66-year-old Schoenbeck, who's been president pro tem since 2021 and has served a total of 14 years over four different decades. The 44-year-old Karr is term-limited in the House after eight years there and is trying to cross over to the Senate. He hopes to win the District 11 seat that Jim Stalzer now holds. Stalzer, 78, is term-limited in the Senate and retiring after 12 years as a lawmaker. Sen. Casey Crabtree Rep. Chris Karr Sen. Lee Schoenbeck The 41-year-old Crabtree is seeking election to a third two-year term. Governor Kristi Noem appointed him to fill the vacancy District 8 seat that Jordan Youngberg resigned on June 17, 2020. Crabtree served the 2023-24 term as Senate majority leader. Karr has a Democratic opponent, Steve Natz. Crabtree's election is uncontested on Tuesday, but he faced a June primary challenge that he easily won against election-integrity advocate Rick Weible 2,057-799. Likewise the House of Representatives speaker, Hugh Bartels, is term-limited after eight years and, now at age 71, is retiring. Traditionally, the speaker pro tem has moved up to speaker in the following term. But Bartels pulled together sufficient support two years ago and scored an upset over Jon Hansen, the 2021-22 speaker pro tem. Rep. Hugh Bartels Rep. Jon Hansen Rep. Mike Stevens Meanwhile, Mike Stevens was elected as speaker pro tem for the 2023-24 term. Now Stevens and Hansen, who are lawyers, look to be on course to compete for the top House spot for the 2025-26 term. The 38-year-old Hansen has served a total of nine years in the House. He won re-election to a second House term in 2012 but resigned the seat on August 15, 2013. He won a third term in 2018 and has been in the House since. The 71-year-old Stevens has been in the House a total of 10 years. He served three terms but didn't seek re-election in 2018. He ran again in 2020 and has been in the House since. Republican ranks in both legislative chambers saw significant shake-ups in June and, depending what happens on Tuesday, there could be many new faces strongly aligned against the carbon-dioxide pipeline that Summit Carbon Solutions plans. Summit wants to collect CO2 from ethanol production plants in South Dakota and several other states, then pipe it to central North Dakota, where plans call for it to be buried. The state Public Utilities Commission last year considered permit applications from two CO2 pipelines and denied both. In turn, the Legislature this year passed SB201 that would change the permitting process for energy transmission facilities, including CO2 pipelines. Under the pending new law, pipelines and transmission facilities would face new financial requirements, such as paying a portion of the landowners' property taxes, as well as a variety of protections for landowners. But any route or transmission facility that receives PUC approval also would no longer be subject "to any local land use, zoning, or building rule, regulation, or ordinance, unless the commission requires compliance with any generally applicable rule, regulation, or ordinance as a condition of the permit issued." Opponents successfully referred SB201 to a statewide public vote. RL 21 will be on the ballot Tuesday. A yes vote supports the pending law's passage, while a no vote opposes it. The attorney general's statement on SB201 doesn't mention the change in the commission's permit process. The CO2 issue was politically costly. Fourteen Republican incumbents lost in the June primaries, including Sen. Jean Hunhoff, whose 24 years make her the Legislature's longest-serving current member. Hunhoff fell to Lauren Nelson of Yankton for the District 17 GOP nomination. Hunhoff voted for SB201, while Nelson spoke out against its passage. Hunhoff's June defeat spurred a mid-July change on the Democratic side of the ballot, with Sarah Carda of Yankton replacing Dennis Menke. Nelson's candidate committee came out of the primary showing a balance of $8,306.44. For the fall campaign, through mid-October, Nelson reported receiving $22,380 of income and spending $30,301.26. She's more recently reported receiving another $1,000 contribution. Carda's candidate committee filed its organizational paperwork on July 23. Two former lawmakers, Democrats Bernie Hunhoff and Ryan Cwach, are her chair and treasurer. (Hunhoff is a brother-in-law of the outgoing senator.) Through mid-October, Carda reported receiving $28,432.63 of income and spending $23,830.31. Since then, she's reported receiving six additional contributions totaling $4,000. Another contest that could tip the Senate Republican leadership is the District 32 battle in Rapid City between incumbent Helene Duhamel, who voted for SB 201, and independent Karen McNeal, who says she doesn't like it. Governor Noem appointed Duhamel to the Senate on December 4, 2019, following the resignation of Alan Solano, and Duhamel has served as a senator since then. The Duhamel campaign committee came into 2024 with a $33,862.10 balance. Through mid-October, Duhamel reported receiving $71,576.97 of income and spending $43,223.60. Since then, she's reported receiving another six contributions totaling $5,000. McNeal established her candidate committee on May 7. Through mid-October, McNeal has reported receiving $17,325 of income and spending $16,880.36. That McNeal poses a serious threat to Duhamel can be seen in many of the contributions that Duhamel has received, including $25,000 from the Crabtree-chaired Senate Republican Campaign Committee -- that was the largest amount the SRCC gave to a candidate this cycle -- and more than $3,000 from a half-dozen Republicans who lost in the legislative primaries. Republicans currently hold a 31-4 majority in the Senate and a 63-7 majority in the House. Republicans are unopposed for 17 Senate seats and are guaranteed to win at least 35 House seats. Democrats on the other hand have one unopposed Senate seat and two unopposed House seats. Among other Senate contests that could affect who's chosen as the chamber's new president pro tem are several in Sioux Falls. In District 12, Republican incumbent Arch Beal faces a challenge from Democrat Clay Hoffman. The 69-year-old Beal, who's served as a lawmaker for 10 years, defeated Democrat Jessica Meyers 4,950-4,237 two years ago. In District 14, Republican incumbent Larry Zikmund is being challenged by Democrat Sandra Henry. The 78-year-old Zikmund has been a lawmaker for 10 years. In 2022, he defeated Democrat Matthew Tysdal 5,854-5,001. In District 15, Democratic incumbent Reynold Nesiba is term-limited after eight years in the Senate and isn't seeking election to the House. He is the Senate's Democratic minority leader. Running for the open seat are Democrat Jamie Smith and Republican Brenda Lawrence. Smith had been the House Democratic minority leader for four years. Noem defeated him in the 2022 governor's election 217,035-123,148. Lawrence meanwhile ran against Nesiba two years ago and lost 3,697-3,310. The full list of 2024 legislative candidates can be found here.