The most contested congressional race in Texas is House District 21, which stretches from South Austin to San Antonio and up into the Hill Country.

Congressman Lamar Smith, who has represented District 21 for more than three decades, announced his retirement last fall. His departure inspired 18 Republican candidates to jump into the race, along with four Democrats hoping to capitalize on President Trump's unpopularity.

Here's What You Need To Know To Vote Early In The 2018 Texas Primary Runoffs

After the March primary, we're down to the final four.

The two Republicans left in the race are Chip Roy and Matt McCall. Roy got 27 percent of the vote in March. The first-time candidate has several years of experience working for elected officials, including Sen. Ted Cruz.

McCall took 17 percent of the vote. He's a Boerne-based entrepreneur in the medical sales field. This is his third attempt to win District 21 and the first time he has made it to a runoff.

KUT's Ben Philpott talks with Jennifer Stayton about the GOP race

On the Democratic side, the race is between Mary Wilson and Joseph Kopser.

Wilson is a minister and math teacher at Austin Community College. She was the surprise winner in the March primary with 31 percent of the vote. She defeated three challengers, including two who were much better funded.

One of those was Kopser. The West Point graduate, Army veteran and businessman took 29 percent of the vote.

KUT's Ashley Lopez talks with Jennifer Stayton about the Democratic race

The two winners in the May 22 runoff will join Libertarian Lee Santos on the ballot in November. Smith won the district by 21 points in 2016; Trump won the vote by 10 points.