It's been 22 years since a Democrat last represented Kansas' 4th congressional district, which is dominated by wheat fields and airplane factories around metropolitan Wichita.

Rep. Mike Pompeo, the district's last congressman who resigned his seat in January to become President Donald Trump's CIA Director, won 61 percent of the vote against his Democratic challenger in November. Two years before that, he managed 67 percent. There's not much swing in this seat.

And yet in the shade of a largely overlooked early spring special election, something of a race has unexpectedly come to boil in the heartland. Pompeo's replacement isn't the slam dunk for the GOP that he should be -- and there's open worry about a surprise on Tuesday night.

"I think it's probably going to be closer than expected," says Todd Tiahrt, the former Republican congressman who held the seat prior to Pompeo. "I think you're seeing the Democratic Party more motivated than Republicans. The average guy in the street that's a registered Republican hasn't really engaged in this race."

State Treasurer Ron Estes, the Republican candidate, is neither offensive nor memorable. In interviews and speeches, he pledges to follow in the footsteps of Pompeo, practice conservatism and "make sure that we change Washington" -- boilerplate fare for red terrain such as this.

His Democratic opponent, James Thompson, is bringing more gusto to the campaign, in part because he has to. A civil rights attorney and Army veteran, Thompson is presenting himself as a nonpartisan candidate in perpetual motion, hitting every diner, saloon and Facebook live chat that offers up a potential vote.

He essentially needs a perfect storm of conjoining events to pull off what would amount to an earth-shattering upset: Low turnout among apathetic Republicans, a determined Democratic base teeming to send a message and an early banked vote that catches everyone off guard.

And even then, it might not be enough.

Late in the game, the cavalry came in for Estes. Sen. Ted Cruz of Texas flew into the district Monday to raise the stakes. "Today, the eyes of the whole country are on Kansas," he said. "Our enemy right now is complacency." Vice President Mike Pence recorded robocalls that hit voters' phones over the weekend; they were buttressed by a "big league" pitch from Trump himself, who said "Estes needs your vote and needs it badly" in a separate phone pitch. The mere fact that the National Republican Congressional Committee was forced to spend a dime on Estes, let alone pour tens of thousands of dollars into television advertising, demonstrates that Thompson's insurgency is real.

It's almost as if Republicans themselves circulated word of an internal poll showing a 1-point race last week as a bright warning flare.

Because of all this, the Kansas special election has become a game of expectations. If Thompson pulls off the upset, it will immediately ignite a national story that will reverberate all the way through next week's other competitive special election in Georgia, where there's a battle for the 6th congressional district seat vacated by Trump's newly appointed Health and Human Services Secretary, Tom Price.

But even if Thompson falls short in Kansas -- by a single-digit margin -- a respectable loss will be interpreted as a rebuke of the Republican Party.

National Democrats will rush to say it is an explicit negative reaction to Trump, a first sign of electoral regret. But the story of Kansas' sleepy 4th congressional district special election may be more about parochial politics.

The president carried this district by a 27-point margin over Hillary Clinton. Thompson has largely avoided Trump as an issue, preferring to raise the stifling unpopularity of Kansas Gov. Sam Brownback, whose deeply conservative agenda has alienated and emboldened a rising moderate electorate in the state.