Republicans maintained their supermajority, however, due to a 2015 rule change that reduced the effective vote threshold to pass legislation from 21 to 19.

Both candidates ran highly negative campaigns, spending millions of dollars on advertisements on what would become the most expensive senate primaries in state history.

She was initially elected in 2014, flipping the seat after incumbent Democrat Wendy Davis retired to run for governor.

[13] Powell advanced to the general election, which saw large spending from conservative groups such as Empower Texans to defend Burton's seat.

[14] Powell narrowly defeated Burton in the general election, flipping the seat back to the Democrats.

Although she was considered potentially vulnerable due to Donald Trump's narrow victory in the district in 2016, she defeated Democrat Rita Lucido in the general election by 5 percentage points.

Flores placed first in the election, a boon to Republicans in the Democratic-leaning district, but he failed to win a majority of the vote, forcing him into a runoff with Gallego.

Incumbent Craig Estes, considered a centrist Republican, faced conservative state representative Pat Fallon in a primary race.

Seliger was considered vulnerable to a primary challenge due to his refusal to back many conservative bills during previous sessions.

He narrowly won his primary in 2014, voted against a 20-week abortion ban, opposed school voucher legislation, and refused to endorse lieutenant governor Dan Patrick's re-election campaign.

He drew two primary challengers, including Mike Canon, whom Seliger had narrowly defeated in 2014 and had the support of conservative groups such as Empower Texans.