If the 2016 results are something of a baseline for next year’s elections, Democrats will face challenges in maximizing their opportunities. In the six Texas districts that House Democrats are targeting, Trump won a majority of the vote in five of them. (Trump won 50 percent of the vote in the district of retiring Rep. Kenny Marchant, 52 percent in the districts of Reps. Chip Roy, Michael McCaul and retiring Rep. Pete Olson, and 53 percent in the district of Rep. John Carter.) Only retiring Rep. Will Hurd’s district is a solid bet to flip. Meanwhile, Democrats face a muddled primary to take on Cornyn, with few of the prospects showing they can match O’Rourke’s early energy in the last cycle.

But if those districts continue to diversify, with college-educated newcomers heading to the state’s booming suburbs for job opportunities, Trump’s narrow victories in the battleground House districts threaten to turn in the Democrats’ favor. In 2018, O’Rourke won a narrow majority of the vote in three of the GOP-held seats in the state, and tallied 49.9 percent of the vote in a fourth.

More importantly, Democrats’ ability to compete in Texas largely hinges on whether Democrats nominate a moderate presidential candidate, like Joe Biden. Biden leads Trump by 4 points, 48 to 44 percent, in a June Quinnipiac poll of Texas voters. Trump led all the other leading Democratic candidates in the same survey. If Democrats nominate a strong candidate at the top of the ticket, it will also help downballot candidates win in tough districts. But if a progressive like Elizabeth Warren emerges from the primaries, Democratic congressional candidates will be forced to distance themselves from their own party’s nominee.