WASHINGTON — The clash over free trade in North America has long been fought over familiar issues: Low-paid Mexican workers. U.S. factories that move jobs south of the border. Canada’s high taxes on imported milk and cheese.

But as Democrats in Congress consider whether to back a revamped regional trade pact being pushed by President Donald Trump, they’re zeroing in on a new point of conflict: Drug prices. They contend that the new pact would force Americans to pay more for prescription drugs, and their argument has dimmed the outlook for one of Trump’s signature causes.

The president’s proposed replacement for the 25-year-old North American Free Trade Agreement is meant to win over Democrats by incentivizing factories to hire and expand in the United States. Yet the pact would also give pharmaceutical companies 10 years’ protection from cheaper competition in a category of ultra-expensive drugs called biologics, which are made from living cells.

Shielded from competition, critics warn, the drug companies could charge exorbitant prices for biologics.

“This is an outrageous giveaway to Big Pharma,” Rep. Rosa DeLauro, a Connecticut Democrat, said in an interview. “The government guarantees at least 10 years of market exclusivity for biologic medicine. It’s a monopoly. It’s bad policy.”

The objections of DeLauro and other Democrats suddenly carry greater potency. The need to curb high drug prices has become a rallying cry for voters of all political stripes. Trump himself has joined the outcry. The revamped North America trade deal must be approved by both chambers of Congress, and Democrats have just regained control of the House.

Rep. Earl Blumenauer of Oregon, the new chairman of the House Ways and Means subcommittee on trade, told The Associated Press that “I don’t think candidly that it passes out of my trade subcommittee” with the biologics provision intact.

“The biologics are some of the most expensive drugs on the planet,” Blumenauer said.

Still, the politics of NAFTA 2.0 are tricky for Democrats and not necessarily a sure-fire winner for them.

The original NAFTA, which took effect in 1994, tore down most trade barriers separating the United States, Canada and Mexico.