(CNN) On its face, a special House election in Kansas should be a walkover for Republicans.

Kansas Republicans control both U.S. Senate seats, all four House districts and the governor's mansion and have massive majorities in the state House and Senate. It's one of the most conservative states in the country and has been for a very long time. (The last time a Democrat represented Kansas in the U.S. Senate was 1938!)

And yet today's special election in Kansas' 4th district -- where Donald Trump won by 27 points last November -- is causing Republicans real concern. Texas Sen. Ted Cruz campaigned on behalf of Republican nominee Ron Estes on Monday and both Trump and Vice President Mike Pence have recorded phone messages urging Republicans to turn out and vote. And the House Republican campaign committee dropped $100,000 on TV ads in the district late last week.

Trump tweeted about the race Tuesday morning, urging voters to get out and support Estes over his Democratic challenger.

"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)," Trump tweeted.

Why the concern? A few reasons.

1) This is a special election. It's April of the year after a presidential election. Turnout is virtually certain to be extremely low, meaning that if one side is more able to get their base out, it could swing the election. "These are first specials of 2017-2018 with a volatile electorate and motivated opposition, [and] we gotta make sure our bases are covered," one Republican strategist closely watching the race told me.

2) The Democratic base is very motivated right now. The election of Trump and his subsequent actions -- from the travel ban to the attempted overhaul of healthcare -- has energized liberal Democrats beyond belief. They will turn out to vote today -- no matter what. Meanwhile, the Republican base is less excited, the by-product of winning everything last fall. That's why conservative stars like Cruz and Pence are all over the district in the final days of the race; they are desperately trying to gin up GOP excitement and turnout.

3) Sam Brownback. The outgoing Republican governor -- he's term limited out of office in 2018 -- is very, very unpopular in the state. Brownback's signature tax reform measures are being rejected even by many Republicans in the state and his six-year attempt at a grand conservative experiment has tarnished the party's brand in the state. Estes, who is the sitting state Treasurer, is struggling to distance himself from Brownback. (Democratic nominee James Thompson has taken to referring to Estes as "Brownbacker Ron Estes.)

4) Trump. Yes, the President carried this Wichita-based seat by nearly 30 points in November. But, this is the first chance any voters in the country have to offer their say at the ballot box since Trump won. If voters -- even Republican voters -- want to send a message to the boss in Washington that what he's doing isn't exactly what they want him to be doing, this is their first chance.

The race was clearly moving in Democrats' favor over its final days. Noted nonpartisan political handicapping site The Cook Political Report moved the race from "Solid Republican" to "Lean Republican on Monday. "Republicans familiar with recent polling describe extremely high Democratic intensity and very low GOP enthusiasm in what is likely to be a very low turnout special," wrote Cook House analyst David Wasserman.

A loss here would be a huge problem for Republicans -- especially considering that they appear to be no better than an even-money bet to hold Health and Human Services Secretary Tom Price's now-vacant seat in another special election next Tuesday in Georgia's 6th district.

Even a narrow defeat for Democrats in Kansas would likely rev up the party base -- and its small-dollar (and big dollar) donors -- in the stretch run in Georgia.

What national Republicans are hoping their spending and attention over the last week will yield is a clear victory for Estes that will tamp down any sort of momentum Democrats are hoping to build heading into Georgia. Democrats, on the other hand, see the Kansas special election as a launching pad for the more winnable seat in Georgia in seven days time.

In short: Kansas, somewhat remarkably, matters to the national political picture.