A defining element of President Biden’s economic agenda appeared to be in new political jeopardy on Thursday, after Sen. Joe Manchin III, one of the chamber’s most pivotal swing votes, said the Senate should take a “strategic pause” on advancing its $3.5 trillion tax and spending package.

Writing in the Wall Street Journal, Manchin (D-W.Va.) raised concerns that the price tag is too high, that the effects on the federal debt might be too great and that the risks of inflation could create financial harm for Americans. He called on his fellow Democrats to slim down their spending ambitions — and to slow down their plans to adopt the measure as soon as this month.

“While some have suggested this reconciliation legislation must be passed now, I believe that making budgetary decisions under artificial political deadlines never leads to good policy or sound decisions,” Manchin wrote.

Manchin previously has expressed misgivings with the size and scope of Democrats’ plans to enact a bill as large as $3.5 trillion. He also has raised past concerns about the deficit, despite assurances from Democratic leaders that their final package will be financed in full.

But Manchin’s calls Thursday for additional time — and a smaller economic package — still created fresh headaches as lawmakers began their work this week to craft what they hope to be a significant overhaul of the country’s education, health-care and tax laws. If Manchin ultimately withholds his vote in pursuit of changes, his party would not be able to proceed in the chamber, since all 50 Republicans have vowed to oppose the bill.

“I have always said if I can’t explain it, I can’t vote for it, and I can’t explain why my Democratic colleagues are rushing to spend $3.5 trillion,” Manchin wrote.

The senator’s comments immediately drew condemnations from liberal-leaning lawmakers in the party, some of whom contend that the $3.5 trillion maximum they are authorized to spend already is far too little to address the challenges the country faces.

“Pause on finally delivering child care, paid leave, education, health care, affordable housing, climate action, and dental, vision, and hearing to millions of families across America? Absolutely not,” Rep. Pramila Jayapal (D-Wash.), the leader of the Congressional Progressive Caucus, tweeted Thursday.

Manchin’s op-ed came a day after he delivered a similar warning shot at a little-noticed event hosted by the West Virginia Chamber of Commerce. The senator cited the uncertainty created by the combination of the coronavirus, the tumultuous withdrawal in Afghanistan and the economic threat posed by inflation as he made the case for his colleagues to “step back” and “see what happens.”

“Everything has changed,” Manchin said, adding that the spending envisioned by Democrats in the package is “not anything we need immediately.”

Democrats are moving forward on their fall legislative agenda, with some in the party pushing for climate crisis measures as part of two key bills. (Blair Guild/The Washington Post)

Manchin also sounded strong opposition to the package’s potential $3.5 trillion price tag. He recounted a story in which he told Sen. Bernie Sanders (I-Vt.), the chief architect of Democrats’ budget, that he is a “hell no” on voting for a bill at that size. And he reiterated his disapproval for some of his party’s proposals to pay for that spending, including Biden’s prior plans to raise corporate tax rates to 28 percent from 21 percent. Manchin previously has endorsed a 25 percent corporate rate.

Manchin’s office on Thursday did not respond to questions about his exact strategy. The West Virginia Democrat oversees a key chamber energy committee, giving him significant influence over the process of crafting portions of the package that are focused on the environment and climate change, a Democratic priority.

For now, Manchin’s public comments evince the broader political conundrum Democrats face in advancing a centerpiece of Biden’s economic vision. With only a narrow majority in both the House and Senate, the party has little room to spare — and significant schisms still to overcome — to transform that proposal into law.

To advance the package, Democrats plan to rely on a maneuver known as reconciliation. In the Senate, it allows party lawmakers to adopt spending legislation using only 51 votes rather than the typical 60. That prevents Republicans from filibustering the bill, which they have described as wasteful, but only if Democrats’ liberal and centrist factions can stay united.

Democrats have articulated an ambitious time frame for adopting the reconciliation bill, aiming to craft legislation by mid-month and adopt it potentially before the end of September. The aggressive schedule is partly attributed to the House, where Speaker Nancy Pelosi (D-Calif.) has agreed to hold a vote on another element of Biden’s economic agenda — a roughly $1 trillion infrastructure plan — by Sept. 27.