Mr. Allred beat the incumbent, Representative Julie Johnson, and is now favored to win the general election in a heavily Democratic Dallas-based district.
Mejia will now serve the remainder of Sherill's term and is seeking a full term in the state's Democratic primary later this year. Hathaway is running for the Republican nomination.
The latest crop of the party’s recruits come from an array of working-class backgrounds, some having worked as farmers and ministers and served in the U.S. military.
"Mistakes were made, and we take full responsibility."