Houston, Texas - Americans cast the first ballots of the primary season on Tuesday, kicking off a midterm cycle that could redraw the political map in Washington – and shape how Donald Trump spends the remainder of his presidency.

Texas anchors the opening slate, with voters in the second-largest state selecting their candidates in high-profile Senate primaries, offering an early test of how both parties position themselves for Trump's final two years.

For Republicans, the priority is steering clear of polarizing nominees who excite the base but repel swing voters. Democrats are debating whether combative, headline-grabbing firebrands or broader populists with cross-party appeal offer the stronger path in the Trump era.

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North Carolina and Arkansas will also pick candidates, with primary winners from across the US facing off in November as voters choose every member of the House of Representatives, 35 of the Senate's 100 seats, and a slew of governors.

The outcome will determine whether Trump continues with a friendly Capitol Hill at his back or faces a Democratic majority empowered to stall legislation and scrutinize his administration.

"Donald Trump is front and center in all of these primaries, whether the candidates like it or not," said Peter Loge, a professor of political communication at George Washington University.

Tuesday's primaries are the first since the US-Israel war on Iran began on Saturday but, with the conflict still in its infancy, it remains uncertain whether it will influence turnout or voter sentiment.

Republicans enter the season defending a 53–47 edge in the Senate and a paper-thin majority in the House.

The headline fight in Texas pits four-term Republican Senator John Cornyn against state attorney general Ken Paxton, a staunch Trump ally who has built a loyal following – despite repeated ethics controversies – by tapping into anti-Washington fervor.

Cornyn, once seen as untouchable, has warned that picking Paxton could jeopardize a seat Republicans are expected to hold comfortably in November, but he is trailing in several polls despite tens of millions of dollars in support from Republican-aligned groups.

On the Democratic side, US Congresswoman Jasmine Crockett and state representative James Talarico are competing for the chance to challenge the Republican nominee – and break a statewide drought that stretches back three decades.

The race has become a test of strategy: Crockett argues her combative style will energize turnout, while Talarico presents himself as a bridge to moderates and disaffected Republicans.

Surveys indicate either race could fail to produce a majority winner, raising the prospect of runoff elections in May.

In North Carolina, another of the country's largest states, Democrats see a Senate race as one of their most promising pickup opportunities.

Polls close there at 7:30 PM, followed by most of Texas at 8:30 PM (9:30 PM ET). Texas typically reports quickly, meaning the contours of several marquee races may emerge within hours.