Donald Trump greets supporters after a rally at Ladd-Peebles stadium on Aug. 21, 2016, in Mobile, Ala. (Mark Wallheiser/Getty Images)

President Trump was swept into office by a populist wave enthralled by his promise of better jobs and a tax cut for the middle class.

But in his first major legislative effort, changing health care laws, he is faced with a bitter populist backlash that has splintered the Republican Party and put his entire agenda on the ropes.

The Senate’s health care bill, which was put on hold Tuesday, would repeal parts of the Affordable Care Act, cap future spending on Medicaid, and cut roughly $700 billion in taxes over 10 years.

Some of these tax cuts would benefit primarily the wealthy, because their capital gains rates would be lowered. And the Medicaid cuts would disproportionately impact the poor, as it is a program run by states and the federal government delivering health benefits for low-income Americans.

The bill would also, according to the Congressional Budget Office, lead to 22 million fewer people having health insurance after 10 years.

When Trump campaigned, he vowed to protect Medicaid from cuts and his top advisers said they would not pursue tax cuts that allowed the wealthy to reduce the overall amount of taxes they pay.

But the House and Senate health care bills reverse both of those pledges. The bills are roundly opposed by Democrats, but Tuesday saw major cracks in the Republican Party’s support, at times invoking arguments often made by Democrats that the bill would help the wealthy at the expense of everyone else.

Sen. Rob Portman (R-Ohio) said he continues “to have real concerns about the Medicaid policies in this bill, especially those that impact drug treatment at a time when Ohio is facing an opioid epidemic.”  Sen. Shelley Moore Capito (R-W.Va.) made a similar point, saying, “I recognize that many West Virginians rely on health coverage and access to substance abuse treatment because of my state’s decision to expand coverage through Medicaid.”

And if Trump and GOP leadership were to try to put some of the safety net spending back into the bill, they'd likely run into opposition from senators such as Rand Paul and Ted Cruz, who are balking at the bill on the grounds that it maintains too much of the Affordable Care Act's coverage outreach.

The rest of Trump’s economic agenda is now sitting on the runway, idling, as the health care bill remains bogged down. Trump had a much more populist message with his plan to overhaul the tax code, because though the bulk of the benefits would go to high-earners, the plan as Trump promises would include rate cuts for virtually everyone. The White House and top lawmakers continue to meet and discuss ways to restructure the tax code, but they have not been able to reach an agreement on key ideas, such as whether the proposal would increase the deficit or be offset by the elimination of tax breaks.

And his goal of creating $1 trillion in new infrastructure projects also has a populist flair. But negotiations on this plan have also been sidelined. Republicans can't agree, for example, how to finance the construction of new roads and bridges. Trump has floated the idea of packaging the infrastructure plan with the tax cuts, but some top advisers have dismissed this ideas as well.

And Congress is expected to try sometime next month to debate ways to raise the debt ceiling, another issue that could unleash a populist backlash, particularly among conservatives.

None of these negotiations has produced a concrete proposal so far in part because the repeated false starts on the health care bill have upended Trump’s entire political approach. Republicans had hoped that the Affordable Care Act’s struggles would help them mobilize broad support for a repeal of the law, but they have struggled to sell their replacement plan amid the populist backlash. CBO’s assessment that, in many cases, both premiums and deductibles would go up made things only worse.

Trump, who doesn’t have as much access to his base of voters as he did during the campaign, is now hearing from lawmakers — both conservative and centrist — who are willing to stand up to him because the backlash for going along with the Senate bill could be severe in their states.

A new NPR/PBS NewsHour/Marist poll found that just 17 percent of Americans support the Senate health care bill and 55 percent disapprove.

Passing changes to government health care programs is politically perilous, and the Affordable Care Act faltered numerous times before it was eventually signed into law. Some of the reluctant Republicans have given Trump signals about what it will take to win their support, suggesting that adding money back into the Medicaid program could be enough to mollify their concerns. For Trump — and the Republicans — to revive this bill, they need to tap back into the populism that helped him win office in November. But, as of now, the populist wave isn’t on their side.