WASHINGTON (AP) — Voters in the Lone Star State will make their second attempt to nominate a Republican candidate for U.S. Senate in a primary runoff election on Tuesday, the electoral version of the Texas two-step.

Also on the ballot are primary runoffs in more than a dozen congressional districts, plus state contests for lieutenant governor, attorney general and others.

U.S. Sen. John Cornyn was the top vote-getter in the March 3 primary, but strong showings by two GOP challengers forced the four-term incumbent to Tuesday's head-to-head matchup with state Attorney General Ken Paxton, the second-place finisher who received President Donald Trump's endorsement on May 19.

The contest is Trump's next opportunity to purge the party of incumbents he views as insufficiently loyal to him and his agenda. It also sets the stage for a general election where Democrats are increasingly optimistic about their chances to score an upset in the heavily Republican state as they look to retake control of the U.S. Senate. Historically, voters have tended to punish the incumbent president's party at the ballot box in midterm election years.

READ MORE: Paxton makes his final pitch in the Texas Senate race against Cornyn, buoyed by Trump's endorsement

The winner will face Democratic state Rep. James Talarico in the general election.

Trump seemed open to endorsing Cornyn following the primary, and he did not excoriate the incumbent in his endorsement of Paxton, as he's done recently with Republican incumbents in Indiana, Louisiana and Kentucky. But he said Cornyn "was not supportive of me when times were tough."

READ MORE: Trump endorses Paxton in Texas Republican primary, boosting effort to oust Sen. Cornyn

Cornyn was critical of Trump ahead of the president's 2024 campaign.

Since much of the Texas primary campaign has focused on the candidates' loyalty to Trump, the counties where the president has the most support could play a decisive role. Although many of the counties Trump won in 2024 with 80% or more of the vote are rural and sparsely populated, collectively they made up about a fifth of the GOP primary vote. Paxton beat Cornyn in these counties, 45% to 40%, while Cornyn performed better than Paxton in the rest of the state.

In counties Trump carried with between 50% and 80% of the vote, Cornyn received about 42% of the vote, edging Paxton by a percentage point. Republican primary voters in the 12 counties Democrat Kamala Harris carried in 2024 preferred Cornyn, 44% to 40%. These counties made up 25% of the overall primary vote, larger than the share of Trump's 80%-plus counties.

READ MORE: Takeaways from the first elections of 2026 midterms

Only two incumbent U.S. senators from Texas have lost a primary in the last 100 years.

In 2025, Republicans redrew the state's congressional districts at Trump's urging as part of an effort to maintain control of the U.S. House.

Among the notable primary runoffs that resulted from the new congressional map, Democratic U.S. Reps. Christian Menefee and Al Green will face each other in the redrawn 18th Congressional District. In the new 33rd Congressional District, Democratic U.S. Rep. Julie Johnson faces a challenge from her predecessor, former Democratic U.S. Rep. Colin Allred.

Here are some of the key facts about the election and data points the AP Decision Team will monitor as the votes are tallied:

When do polls close?

Polls close statewide at 7 p.m. local time, which is 8 p.m. ET and 9 p.m. ET. Most polls are in Central time and close at 8 p.m. ET, while polls in the westernmost part of the state are in Mountain time and close at 9 p.m. ET.

What's on the ballot?

The AP will provide vote results and declare winners in Republican primary runoffs for U.S. Senate, U.S. House, railroad commissioner, Court of Criminal Appeals, state Senate and state House and in Democratic primary runoffs for U.S. House, lieutenant governor, attorney general, state Board of Education and state House.

Who gets to vote?

Voters who did not participate in a party primary on March 3 may vote in the runoff for either party. Voters who did cast a ballot in a party primary may only vote in the runoff of the same party as they did in the primary. In other words, Democratic primary voters may not vote in a Republican primary runoff or vice versa. Voters in the non-partisan primary may vote in either party's runoff.

How many voters are there?

As of the March 3 primary, there were nearly 19 million registered voters in Texas.

How many people actually vote?

About 2.2 million Republican primary votes and about 2.3 million Democratic primary votes were cast in the March 3 Texas primary.

In the 2022 Republican primary for Texas Attorney General, turnout was about 1.9 million voters in the primary and about 932,000 in the primary runoff.

How much of the vote is cast early or by absentee ballot?

About 63% of the vote in the March 3 Republican primary was cast before primary day.

As of Thursday, about 621,000 Republican primary ballots and about 262,000 Democratic primary ballots had already been cast in Tuesday's election.

When are early and absentee votes released?

Counties tend to release all or nearly all results from early and absentee voting in the first vote update of the night, before any in-person Election Day results are released.

How long does vote-counting usually take?

In the U.S. Senate primary in March, the AP first reported results at 8 p.m. ET just as polls closed in most of the state. By 11:39 p.m. ET, 75% of the vote had been counted. Vote results were released continuously until about 5:58 a.m. ET, with about 98% of the total vote counted.

When will the AP declare a winner?

The Associated Press does not make projections and will declare a winner only when it's determined there is no scenario that would allow a trailing candidate to close the gap. If a race has not been called, the AP will continue to cover any newsworthy developments, such as candidate concessions or declarations of victory. In doing so, the AP will make clear that it has not yet declared a winner and explain why.

How do recounts work?

Texas requires an automatic recount only in cases of a tie vote. Losing candidates may request and pay for a recount if the margin is less than 10% of the leading candidate's vote. The AP may declare a winner in a race that is subject to a recount if it can determine the lead is too large for a recount or legal challenge to change the outcome.

Are we there yet?

As of Tuesday, there will be 161 days until the 2026 midterm elections.