Earlier this month, a senior White House official deeply involved in enacting President Trump’s agenda on Capitol Hill laid out the Administration’s ideal legislative schedule for the rest of this year.

“Between now and the August recess, we’d like them to get health care done, we’d like them to get the debt ceiling done, we’d like them to start tackling the budget,” he told me. “So when they get back from the August recess, first or second week of September, we can throw a tax proposal down and, literally, we can do taxes for September, October, and November.”

The G.O.P. has adopted a major—even radical—agenda: transforming a massive sector of the economy, slashing taxes and rewriting the entire tax code, passing a budget that would dramatically reduce the size of government, and, in the middle of all of that, raising the debt limit. They have a plan to accomplish almost all of it before the end of the year, with minimal transparency, and without relying on a single Democratic vote. But if health-care reform goes down this summer, the rest of the plan may sink with it.

For obscure parliamentary reasons, Republicans can’t move on with the rest of their wish list until they pass the health-care bill. And those prospects are not looking good. On Tuesday, Mike Lee, of Utah, became the fifth Republican senator to say that he would vote against even bringing the health-care bill up for debate. Senate Majority Leader Mitch McConnell, who announced, also on Tuesday, that he will delay the vote until after the July 4th recess, may yet broker a deal on health care, but if he fails to do so the legislative impact for Trump could be calamitous.

The parliamentary maneuver McConnell is using is called reconciliation. The process was created, in 1974, as a way to streamline the congressional budgeting process. It wasn’t intended to be used for major legislative changes. However, as partisan deadlock has grown, it has become an increasingly attractive legislative tool because it is protected from a filibuster in the Senate and therefore needs only fifty, rather than sixty, votes to pass. (Vice-President Mike Pence can cast a tie-breaking vote in both cases.)

Bill Clinton’s attempt at reforming health care was probably doomed the day that he decided not to use reconciliation. Obama passed his initial health-care bill through the Senate without using reconciliation, but he always kept it as a backup plan—and it turned out that he needed it. When he lost his sixty-vote majority in the Senate, Democrats used the process to pass a final package of tweaks to the bill.

This year, Republicans have been even more creative. They planned to use one reconciliation bill for health care and a separate one for the beast of tax reform. But one of the many arcane rules about the reconciliation process is that any new reconciliation bill cancels out the old one. “This is the first time anyone has tried to do this,” Stan Collender, a longtime budget expert who now works for the strategic-communications firm MSLGROUP, said. “You can only have one budget resolution in effect at a time. Their idea was to do health care and then move on to tax reform, but that strategy was based on doing health care quickly.”

If the Senate health-care bill dies and Republicans move on to tax reform, they will have an interesting choice to make: do they give up on health care and propose only a tax-reform bill? Or do they combine tax reform and health care into one monster bill, which would make passage even more daunting?

Some of these procedural issues might be overcome by a kind of nuclear option, whereby Republicans ignore or find a way to overrule the Senate parliamentarian who enforces the budget rules. But, however health care is resolved, the rest of the items on the Trump agenda consist of a series of fiendishly difficult political issues that divide Republicans. The budget, which must be resolved by October 1st, will pit congressional Republicans, who have decried the White House’s proposed budget, against Trump, who was so miffed about being ignored during the budget negotiations earlier this year that he tweeted, “Our country needs a good ‘shutdown’ in September to fix mess!” Republicans in the House are comfortable with defaulting on the debt, and the President himself has called for a shutdown. Things could quickly grow ugly.

In the middle of this drama, the White House wants to pass a comprehensive tax-reform bill. The last time Congress approved such a piece of legislation was in 1986, and it was the result of a lengthy and bipartisan process of hearings and horse-trading. So how are Republicans approaching tax reform this year? They are writing a bill in secret that they intend to pass using reconciliation. The group writing it, which calls itself the Big Six, consists of Steve Mnuchin, the Treasury Secretary; Gary Cohn, Trump’s top economic adviser; Representative Kevin Brady, the chairman of the House Ways and Means Committee; Orrin Hatch, the chairman of the Senate Finance Committee; House Speaker Paul Ryan; and Senate Majority Leader Mitch McConnell. There are no Democrats and no women involved, and there have been no hearings.

“We are all on the same page,” the senior White House official told me, referring to tax reform. “There's going to be one tax bill and one tax bill only.”

Before a tax bill can move forward, Republicans will have to agree on health care—or abandon the issue. The health-care reconciliation package is a giant iceberg that needs to be cleared out of the way before Republicans can move forward with the rest of their agenda.