By the time Dr. Hector Gonzalez arrived in Laredo, Texas, in 2001, the last abortion clinic had already closed. He spent the next 20 years experiencing firsthand where the largely Hispanic and heavily Catholic community along the border with Mexico usually sided.

“Definitely it was, ‘No abortion,’” said Gonzalez, the city’s former public health director.

That culture has helped protect the region’s nine-term congressman, Henry Cuellar, who is one of the last anti-abortion Democrats in Congress. But he’s facing the stiffest challenge of his career on Tuesday in a runoff election against progressive rival Jessica Cisneros, a 28-year-old immigration attorney who supports abortion access.

With the U.S. Supreme Court poised to potentially overturn abortion rights in a ruling this summer, the runoff is being closely watched for clues about whether the issue will animate Democratic voters. An infusion of money that outside groups have poured on the ground and across TV in South Texas is an indicator of an important race, with abortion rights advocates trying to lower expectations about broader implications.

“National trends are not set by one election and not determined by one election,” said Laphonza Butler, president of Emily’s List, which backs women who support abortion rights and has endorsed Cisneros.

Regardless, the race will provide insight about the direction of the Democratic Party. Progressives have scored some notable wins so far this primary season, defeating a moderate candidate in last week’s Senate primary in Pennsylvania and potentially unseating an incumbent congressman in Oregon, where vote counting is still underway.

Eager to protect an incumbent, House Speaker Nancy Pelosi has stood by Cuellar even as she reaffirms her staunch support of abortion rights. Rep. Jim Clyburn, the third-ranking Democrat in the House, campaigned with Cuellar in Texas this month, saying the most important priority should be keeping the seat in the party’s hands. Cisneros, he argued, was at risk of losing to a Republican.

Still, a leaked draft of the court’s ruling in April has shaken up what was already a close — and increasingly costly — race. In the March primary, Cisneros finished roughly 1,000 votes behind Cuellar, forcing the runoff after neither candidate met the majority threshold to win outright. It was as close as Cuellar has come to losing his 17-year grip on the seat.