Image copyright Getty Images

On Tuesday people in Kansas' fourth congressional district, an area that includes the city of Wichita, voted in a special election for a new congressman. They chose the state treasurer, Ron Estes, a Republican, over James Thompson, a Democrat and a civil rights lawyer.

It was a victory for Estes and for other Republicans in the state. As it happened, he had support from influential people - and from one in particular - who lived outside of his congressional district.

"A wonderful guy," Trump tweeted about Estes on Tuesday. "I need his help on Healthcare & Tax Cuts (Reform)."

Trump was interested in the race - in part because he was responsible for it.

The special election was called because Trump had asked the district's previous representative, Mike Pompeo, a Republican, to become CIA director. After Pompeo was confirmed in his new post, Kansans went back to the polls so they could choose a new representative.

Image copyright Alamy Image caption Ron Estes was elected by a narrow win

People in Kansas and elsewhere saw the election as a referendum on the Trump administration: a victory for Estes meant that people in Kansas and other parts of the Midwest still supported the president.

A defeat for Estes, however, would have meant that the people who lived in the district - and perhaps in other parts of the Midwest, too - were unhappy with the president and with Republicans in the state.

The fourth congressional district - like most of the surrounding area in south central Kansas - is rock-solid Republican. The state itself is located in the heart of Flyover Country, a Midwest region that many people see only from planes when traveling from one coast to the other.

People in Kansas and other states in the Midwest may be invisible to some of those who live on the coasts, yet the Midwesterners have power: they propelled Trump to victory in November.

Image copyright Getty Images Image caption Trump recorded a "robo-call" in support of Estes

For this and other reasons, it's a good idea to watch the voters in Kansas. Located in the middle of the country, they often act as a signpost, revealing how people in the US feel about politics and where the country is heading.

Victoria Snitsar, a student at the University of Kansas who lives in Lawrence, supported Estes' message of fiscal conservatism and knocked on doors for him in Wichita during the campaign. She said she believed his victory meant "people are holding on to the president's message".

Estes was elected by a smaller margin than many Republicans would have liked, however. While Trump won with the distrcit overwhelmingly, Estes received 53% of the vote, while Thompson won 46%, and another candidate, Chris Rockhold, who was running as a libertarian, won less than 2%.

It was a narrow victory, and it hinted at a darker mood.

"Estes underperformed Trump's margin by 20.3 points," wrote FiveThirtyEight's Nate Silver on Twitter. "If every district behaved like that, Dems would gain 122 (!) House seats next November."

Not everybody in Kansas has been thrilled with the Trump administration and the way they've been running the government. In addition many Kansans have been unhappy with Gov Sam Brownback, a Republican, and his drastic cuts in education spending and social services.

"There's some discontent," said Mike O'Neal, a Republican consultant who used to work for the Kansas Chamber of Commerce. Whether that blows over or becomes a problem for Republicans remains to be seen.

In the meantime political operatives will continue to watch people in Kansas, hoping to gauge the nation's mood.