OKLAHOMA CITY (AP) — Six Republicans entered Tuesday’s Oklahoma primary confident that their party could win an open congressional seat currently held by a Democrat, and three Democrats went into the election hopeful they could retain the seat in a state that has grown overwhelmingly conservative.

Three incumbent Republican congressmen were facing challengers within their party Tuesday, while Democratic voters were choosing candidates to challenge two of those congressmen. Drawing the most attention is the fight for a seat held by retiring Rep. Dan Boren — the only Democrat in Oklahoma’s congressional delegation — which also will feature an independent on the November ballot.

Democrats had dominated Oklahoma politics since statehood, but Republicans gained a majority in the state House in 2004 and then the state Senate in 2008. Boren’s 2nd Congressional District sprawls across 26 counties in eastern Oklahoma, bordering Kansas, Arkansas, Missouri and Texas.

“There’s always that stigma about Democrats playing there (in Oklahoma). But at the same time, it’s Dan Boren’s seat, so it’s definitely something we’re watching and something we’re paying attention to,” said Stephen Carter, spokesman for the Democratic Congressional Campaign Committee in Washington, D.C. “I think the Democrats that are running there fit the district profile.”

Polls will be open from 7 a.m. to 7 p.m.

Because Oklahoma’s primary election date this year is earlier than usual and there are no statewide Democratic primaries in a state where registered Democrats still outnumber Republicans, many political experts predict turnout will be light.

“There are isolated pockets throughout the state where there’s either a hot, local race that will drive interest and turnout, but for large portions of the electorate, there’s only maybe one race to vote on or maybe even none in the primary,” said Democratic political strategist Ben Odom.

Another interesting dynamic to this year’s elections is the rise of tea party-aligned candidates who are challenging incumbents, in many cases complaining that the GOP officeholder is not conservative enough.

Incumbent Republican U.S. Reps. John Sullivan of Tulsa, Frank Lucas of Cheyenne and Tom Cole of Norman are all facing primary challenges from fellow Republicans, as are more than a dozen Republican incumbents in the state House and four in the Senate. And many of the state legislative races have turned particularly bitter.

“Do I wince a little bit, sure, but campaigns are about contrast, whether it’s Republican versus Republican or Democrat versus Democrat,” said Oklahoma Republican Party Chairman Matt Pinnell. “Certainly we don’t like it to get too heated or too confrontational, but that’s going to happen, especially in this environment.

“There’s a lot of passion out there, a lot of people are fired up. They can’t wait for November to get here, and in this type of climate, you can get these kinds of primaries.”

Democrats seeking Boren’s congressional seat include Earl Everett, 78, a retired schoolteacher from Fort Gibson; Wayne Herriman, 59, the owner of a Muskogee-based seed company; and Rob Wallace, 48, a former state and federal prosecutor from Fort Gibson.

The six Republicans are three-term state Rep. George Faught, 49, of Muskogee; business owner Markwayne Mullin, 34, of Westville; former Edmond state Rep. Wayne Pettigrew, 49, of McAlester; attorney and former Tishomingo Mayor Dustin Rowe, 36; Fort Gibson minister Dwayne Thompson, 54; and retired Marine Corps officer Dakota Wood, 49.

Democratic primaries will be held in the 3rd and 4th congressional districts, seats currently held by Lucas and Cole, respectively.

A primary runoff will be held Aug. 28 if no candidate captures more than 50 percent of the vote.

The only statewide election on the ballot Tuesday is a Republican primary for a full, six-year term on the Oklahoma Corporation Commission. The three-member panel regulates public utilities and the oil and gas and intrastate transportation industries. Commissioner Bob Anthony, Oklahoma’s longest serving statewide elected official who was first elected in 1988, faces a challenge from former commission administrator Brooks Mitchell.

Turnout for early voting has been varied across the state. In Cleveland County, for example, Election Board Secretary Jim Williams said only about 350 voters cast ballots through Monday afternoon, the last day of Oklahoma’s three-day early voting period.

But in Rogers County, located in the heart of the 2nd Congressional District, nearly three times as many voters cast in-person absentee ballots by Monday afternoon than they did for the presidential primary election in March, said Rogers County Election Board Secretary Julie Dermody.

“There’s a lot going on here that I think is generating some of that turnout,” Dermody said.

In many areas, state legislative or county races will help drive turnout. The primary winners in 13 House races — 12 Republicans and one Democrat — will be sworn into office, since no candidate in the opposing party filed for those seat. Tuesday’s elections also are expected to determine the next state senator in four districts where Republicans were the only candidates to file.

However, some of those House and Senate primaries could continue to the August runoff if no candidate gets more than 50 percent of the vote.

Republicans currently have a 32-16 advantage in the Oklahoma Senate and a 67-31 edge in the House, with three seats currently vacant.