OKLAHOMA CITY — The makeup of Oklahoma’s congressional delegation and whether Democrats can stave off a GOP sweep of the state’s federal elective offices hangs in the balance as voters head to the polls.

Republicans hope to capture all five of Oklahoma’s U.S. House seats for the first time ever Tuesday. Besides the battles for those seats, voters also will be casting votes for president and deciding the fate of six state questions.

With two Republican U.S. senators already in place and not up for re-election, the Oklahoma GOP is looking to take over the only blue section of the state’s congressional map that remains: the sprawling 2nd Congressional District in eastern Oklahoma.

The Democrat who currently holds the 2nd District seat, U.S. Rep. Dan Boren, announced last year he wouldn’t seek a fifth term in office.

In the race to replace Boren, Republican Markwayne Mullin, a 35-year-old plumbing company owner from Westville, faces longtime state and federal prosecutor Rob Wallace, 49, of Fort Gibson. Independent Michael Fulks of Heavener also is in the race.

Donna Jones, a nurse from Muskogee, said she initially preferred Mullin for his small-business background, but ended up voting for Wallace.

“I just didn’t like Mullin’s attack ads,” said Jones, 57.

Teresa Scott, a 55-year-old small business owner, said she voted for Mullin because of his platform.

“Him being against Obama, that was a big plus,” Scott said.

There’s also an open congressional seat in northeast Oklahoma’s 1st District, which includes Tulsa, after Republican Navy pilot Jim Bridenstine, 37, knocked off incumbent U.S. Rep. John Sullivan in the GOP primary. Bridenstine now faces Democrat John Olson, a 35-year-old Army reservist and small businessman, and independent Craig Allen, 54, of Tulsa. A Democrat hasn’t been elected to that seat since 1972.

Democrats have fielded a candidate in each of the state’s other three congressional districts, but those races feature strong incumbents in U.S. Reps. Frank Lucas in the 3rd District, Tom Cole in the 4th District and James Lankford in the 5th District.

Lucas, of Cheyenne, faces Democrat Timothy Ray Murray of Guthrie and independent William Sanders of Stillwater. Cole faces Democrat Donna Bebo of Fletcher and independent R.J. Harris of Norman. Lankford, running for re-election for the first time, faces Democrat Tom Guild of Edmond and two independents — Pat Martin of Jones and Robert Murphy of Norman.

At the state level, Republicans are expected to maintain or build upon their majorities in the House and Senate. The GOP currently enjoys a 32-16 advantage in the state Senate, and already has added two seats by virtue of Democrats failing to field candidates in two districts where Democratic incumbents are stepping down. Republicans also are competing for three open seats previously held by Democrats, while defending just two Republican-held open seats.

In the House, where Republicans enjoy a 67-31 advantage with three seats vacant, there are 34 seats up for grabs in Tuesday’s election. Sixteen Republican incumbents are facing challenges, along with seven Democrats. Eleven seats are open.

Each Oklahoma voter also will have a chance to decide six state questions and whether to retain judges on the state’s appellate courts.

The measures cover issues including whether to abolish affirmative action programs in state government and whether to eliminate the intangible property tax businesses pay for such things as patents, trademarks and brand names.

Other state questions target property tax increases, the governor’s role in the parole process, oversight of the Department of Human Services, and whether the Oklahoma Water Resources Board can issue bonds.