No Democrat has won this seat since 1992, the year Bill Clinton defeated George H.W. Bush. "A win is a win but this should have been relatively simple and it wasn't".
But Thompson benefited from Trump's low approval ratings, a deeply unpopular Republican governor and a state GOP that has been hampered by infighting.
Dominating the outside spending in these races are the Congressional Leadership Fund, a super political action committee linked to House GOP leaders, and the National Republican Congressional Committee, a national party committee. The open seats are in Georgia's 6th District, Montana's at-large district, South Carolina's 5th District and California's 34th District.
In this March 23, 2017, photo, Democrat James Thompson, a candidate for Kansas' 4th Congressional District, speaks during a debate in Wichita, Kan.
But that was hardly the case.
President Trump, who carried the 4th district with about 57 percent of the general election vote in 2016, also pushed for Estes, with a message on social media network Twitter expressing support for his fellow Republican earlier in the day.
That's a relatively small margin in Kansas' right-leaning 4th district, which Trump won by 27 points and Pompeo won by more than 30 points in November. Wichita is home to Koch Industries, the company led by conservative billionaire political donors Charles and David Koch.
Thompson spokesman Chris Pumpelly said Estes' victory required recorded calls from Trump and Vice President Mike Pence and other help from Republicans nationally.
Bernie Sanders" former presidential campaign team, now running a group called Our Revolution, piled on: "The Democratic Party can no longer ignore districts that they consider "safe' for Republicans".
"Estes underperformed Trump's margin by 20.3 points", wrote FiveThirtyEight's Nate Silver on Twitter.
Though it's far too early to know whether those Democratic gains will hold through the 2018 midterm elections, Kansas was an ominous sign for the GOP ahead of a much closer Georgia 6th District special election next week in Atlanta's northern suburbs - as well as other upcoming special elections in Montana and SC. Still, the National Republican Congressional Committee spent almost $100,000 on ads in the final days of the race. Both parties treated it as such and that's how the voters perceived it.
"We set out about 60, 75 days ago with people who told us we didn't stand a snowball's chance in hell of winning. That's why he's raising expectations on himself".
"Everybody's internal numbers on both sides didn't have this being a race in time to start a field operation", said Ian Russell, who served as DCCC's political director a year ago. A ton of seats would come into play that no one ever dreamed of contesting-more than enough to flip the House.
"Some people are saying you know, 'I'm a little nervous I don't know what to do, '" Lewis said on MSNBC while discussing why Democrats should stay engaged and organized to challenge the Trump administration and Republican lawmakers.style="text-align: center;"