A dark-money group created by allies of President Joe Biden released an ad last month thanking Arizona senator Kyrsten Sinema for pushing to lower prescription drug prices — just before she told the White House she will oppose Democrats’ drug pricing plan.

While Sinema previously campaigned on a pledge to reduce drug costs, the freshman senator and one-time-progressive-turned-corporatist has emerged as the chief roadblock to Democrats’ plan to allow Medicare to use its bulk purchasing power to negotiate significantly lower prescription drug prices. Because Democrats hold a narrow 50-50 majority in the Senate, they cannot afford to lose any votes on the measure.

In early August, Building Back Together, a nonprofit created to support Biden’s agenda, announced it was launching a $10 million ad campaign to build support for Democrats’ infrastructure plans while lawmakers were out of town on a long summer recess period.

“The goal, officials said, was to bombard the home districts of members of Congress with ads — both televised and digital — to keep the pressure on to follow through on their votes as well as to underscore much of the agenda’s popularity with the public,” the Associated Press reported at the time.

One of the ads released by Building Back Together thanked Sinema and her counterpart, Senator Mark Kelly, for working to reduce drug prices.

“President Biden and Senators Kelly and Sinema delivered for us,” the ad says. “They’ve pulled our economy back from the brink, and now they’re fighting to create millions of good-paying jobs and lower the costs of health care, childcare, and prescription drugs. Thank Senators Kelly and Sinema for delivering for Arizona.”

Clearly, the ad campaign failed.

Earlier this month, Sinema informed the White House of her opposition to the drug pricing plan, days after a Big Pharma–funded front group started running television, radio, and digital ads calling her a “bipartisan leader” and an “independent voice for Arizona.” The front group has already spent roughly $600,000 boosting Sinema on the Arizona airwaves, according to data from AdImpact.

Over the course of her career, Sinema has raised more than $500,000 from donors in the pharmaceutical and health-products industries, according to OpenSecrets.

Now, Sinema is threatening to tank both infrastructure bills — the bipartisan, industry-friendly deal she helped negotiate and Democrats’ broader $3.5 trillion reconciliation spending package meant to fund Biden’s economic, health, and climate agenda — if Democrats don’t pass her bill first.