Kansas special election becomes test for Trump and GOP Democrats hope the election will give evidence of an anti-Trump wave in 2018.

 -- Republicans are making a big last-minute push in a special election in a rural Kansas district that is getting too close for the GOP's comfort.

It is the first congressional race since November, and Republicans hope for a landslide victory in a district that President Trump won by nearly 30 percentage points. The House seat was vacated when Rep. Mike Pompeo became the director of the CIA in January.

Democrats want to perform well enough to show that anti-Trump sentiment could prompt a blue wave in the 2018 House and Senate races.

Republicans have held the seat, for Kansas' 4th Congressional District, in south-central Kansas, for more than two decades.

Who's running?

Republican Ron Estes, the state treasurer, has been expected to defeat Democrat James Thompson, a local civil rights attorney and military veteran, in this election. But in the race's home stretch, Republicans have rushed resources and star power into the district.

What are signs that Republicans may be getting nervous?

Democrats are hoping for an upset victory or even a close finish in this very red district, and the national GOP has made moves possibly indicating that the race is closer than expected.

Tea party favorite Ted Cruz held a rally with Estes in the district Monday afternoon. President Donald Trump and Vice President Mike Pence recorded robocalls for Estes' campaign.

In the president's call, he said that Estes is "a conservative leader who's going to work with me to make America great again ... Ron is going to be helping us, big league."

Bringing in the big guns: President Trump recorded a robo-call for Ron Estes today in #KS04. Listen here --> https://t.co/GjxoGGZdPt

Trump also tweeted about the race on Tuesday morning.

Ron Estes is running TODAY for Congress in the Great State of Kansas. A wonderful guy, I need his help on Healthcare & Tax Cuts (Reform). — Donald J. Trump (@realDonaldTrump) April 11, 2017

The GOP group dedicated to House elections, the National Republican Campaign Committee, put more than $100,000 in advertising into the race in the week before the election. And House Speaker Paul Ryan made a fundraising request for Estes' campaign, according to The Kansas City Star.

"As a friend of Ron's and as House speaker, I can tell you that this one of the most important House races in the country. Please consider this a personal request," Ryan wrote, according to the Star.

What would a close finish mean for national politics?

A narrow GOP victory — or a Democratic upset — could be a red flag for the GOP for other 2017 elections, such as the hotly contested House race in Georgia next week and elections for governor in Virginia and New Jersey.

Anything short of a resounding GOP win could demonstrate that anger over Trump's victory or his policies has mobilized liberal and moderate voters or that the bumps of the administration's first 100 days has tempered enthusiasm among Republicans.

Regardless of the outcome, this is only one election, with plenty of local dynamics at play, such as the unpopularity of Gov. Sam Brownback and the campaign run by Estes.

Why could this race be closer than expected?

Though a brighter spotlight has been on Georgia's special election next week, national Democrats have targeted efforts on the Kansas seat. The Daily Kos said Democrats raised more than $100,000 in two days last week after reports that national Republicans were dropping more money into the Kansas race.

Estes has been a member of the governor's team, and Brownback's unpopularity contributed to GOP losses in the state's 2016 legislative elections. Thompson has worked to paint Estes as Brownback's right-hand man.

Estes' fundraising advantage over Thompson was lackluster — $283,000 for Estes, versus $252,000 for Thompson, according to the latest complete campaign finance report, in late March. Thompson said he has gotten support from grass-roots activists and has painted Estes as getting his money from out-of-district sources.