(Bloomberg) — President Joe Biden is set to ratchet up pressure on congressional Democrats on Thursday, as discord within the party threatened to derail key pieces of his economic agenda, including lowering prescription drug prices and some of his proposed tax hikes on the wealthiest Americans.

According to a White House official, Biden is expected to call for Democrats’ unity in a speech on Thursday. He will focus his attention on the difficulties of middle-class families, including the high prices of prescription drugs and hearing aids as well as general costs associated with raising children. 

The recent back-and-forth on Capitol Hill has shown the limits of Biden’s power to guide the $3.5 trillion plan through a narrowly divided Congress. Moderate Democrats balk at the recent attempts to negotiate drug prices and impose a new income tax on the richest people. These are measures progressives support.  

For the package to be passed, the White House cannot afford to lose support from three House Democrats. It needs the full support of all Democratic senators. 

Biden met with two conservative Democratic senators, Joe Manchin from West Virginia and Kyrsten Silena from Arizona. They had separate meetings at White House. Manchin has pushed for a spending package less than half of Biden’s proposal, a move that risks delaying the president’s package by weeks or months in Congress with tax, health care and other issues still unresolved. 

White House aides have spent the last several days negotiating and speaking with lawmakers and top staffers to weigh various options to raise enough money to fully fund Biden’s plan and ensure as many big policies as possible survive the legislative process.

Progressives have been disappointed as House Democratic lawmakers shied away from ideas like taxing the increase of wealthy people’s assets at death — a key pillar of Biden’s attempts to reduce income inequality. A few moderate Democrats backed out of efforts to lower the price for prescription drugs this week after intensive lobbying by the health-care sector.

Democratic Representatives Kurt Schrader, Scott Peters from California, Kathleen Rice and Kathleen Rice both of New York voted against the bill that allowed the government price controls and allows drugmakers to lower their prices. After a tied vote in the committee, the measure did not advance.

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