A Democratic aide in the room disputed that the debate became heated, noting that the discussion focused on a technical aspect of the legislation — whether or not the legislation actually eliminates a longstanding ban on Medicare negotiating prices directly with drug companies.

Democratic leaders have touted their legislation as lifting the ban on negotiations. But in reality, the bill only creates an narrow exception to the clause — a minor difference that some Democrats worry could fuel attacks down the road for overselling one of its core provisions.

“It’s very technical, and that’s why there was a back-and-forth, because it’s so complicated,” the aide said.

The bill would require the federal government to negotiate prices on at least 35 high-cost medicines, achieving a longtime policy goal for liberals. But some progressives have argued that most drugs would never be negotiated under the current plan, and worry that Democrats might oversell their legislation.

DeLauro said after the meeting that she is still waiting to see the final version of the bill, which will go through its third and final markup on Tuesday. She acknowledged “there are questions about the numbers of drugs covered.”

“Overall, it is a giant step forward. We’re taking on the issue of prescription drugs, whereas others are just talking about it,” DeLauro said in a brief interview. “The administration talks out of both sides of its mouth on this issue. Democrats are looking for a proposal, which is what we promised to do.”

She later told POLITICO in a statement that she was seeking clarity on an aspect of the prescription drug bill during Tuesday's caucus meeting and intends to vote for the bill.

"I fully stand behind our efforts to help the tens of millions of people suffering from skyrocketing prescription drug costs," she said. "We are taking action for the people as the Trump administration talks a big game but does nothing.”

The caucus meeting debate came as Democratic leaders fought behind the scenes to put down a separate insurrection led by progressive Rep. Lloyd Doggett.

Ahead of a final markup of the legislation on Tuesday, the Ways and Means Committee chairman had encouraged the panel’s Democrats not to push for any further changes – a bid to keep it on track for a floor vote by the end of the month, according to several lawmakers and aides familiar with the discussion.

But Doggett, who has repeatedly criticized the bill as too timid, insisted on pressing ahead with a series of amendments aimed at pushing the proposal further left. And in what multiple sources described as an effort to force the committee’s hand, Doggett refused to share those changes with the rest of the committee until late on Monday night.

Democratic leadership responded by urging Democrats on the committee to unanimously reject all of Doggett’s amendments – a retaliatory move that multiple sources said upset some members who saw a political upside in supporting some of the tweaks aimed at further lowering drug prices.

The planned amendments include full lifting of Medicare’s negotiation ban – which proponents noted was central to Democrats’ “Better Deal” platform during the 2018 election cycle. A second would make the lower prices negotiated by the federal government available to the uninsured, in addition to seniors and private health plans.

That left some Democrats on the committee feeling cornered on Tuesday -- scrambling during the markup's opening hours to decide how to react if Doggett seeks votes on each of his proposed changes, and debating the merits of bucking leadership’s direction in order to support a handful of politically popular amendments.

“He doesn’t want to go against leadership, but doesn’t want to vote against the good amendments like making these lower prices available to everybody,” said one staffer for a Ways and Means Democrat. “I think that’s where a lot of people are.”

Progressives have long argued that House Democrats should draft the boldest possible drug pricing bill to tout to the base. But other Democrats — including dozens of moderates serving in formerly GOP seats — have argued the House should tee up only legislation that stands a chance in the Senate.

Senate Majority Leader Mitch McConnell (R-Ky.) said previously that Pelosi’s drug pricing plan won’t be considered in the Senate.

But on Tuesday, some Democrats warned that the further changes pushed by progressives now risk splitting the caucus, potentially threatening their ability to simply get the legislation through the House.

“It’s hard enough to get 218 of us on the same page, on the same day, on a complicated issue,” said Rep. Dan Kildee, a member of House Democrats’ whip team. “Anything that makes that less certain means we’re more interested in the value of our own ideas than the people that we profess to care so much about.”

That fight echoes a much broader debate that has consumed the caucus for months: whether to draft legislation to cater to the progressive base, or seek common ground with Republicans in hope of sending something through the Senate.

For moderate Democrats, especially those in the most GOP-leaning districts, the prescription drug pricing bill has taken on even more significance as the House enters the second month of an impeachment inquiry into President Donald Trump.

Moderating the bill in hopes of appealing to Republicans is a futile effort, Doggett warned his colleagues at the Ways and Means markup. Instead Democrats should be ‘setting a solid foundation,” for a future administration and Congress.

“Some see to think that if this bill is sufficiently narrow President Trump will … embrace the bill,” Doggett said. “But [Republicans‘] total war against the proposal … and [Trump’s] erratic behavior suggest that that is not very realistic.”

Sarah Karlin-Smith contributed to this report.

