“I have to tell you, it’s an unbelievably complex subject,” President Donald Trump told a group of governors at the White House yesterday. “Nobody knew that health care could be so complicated.”

Trump is not an overly complicated rhetorician. He uses a few key phrases—call them Trumpisms—to convey ideas that he wants listeners to believe are universal. When he uses the often mocked expressions “many people are saying” or “a lot of people think,” for example, what he really means is that he is about to say something that he personally believes, which may not have any factual foundation, such as his comments about widespread voter fraud in the 2016 election or the size of crowds at his events.

“Nobody knew” is Trumpspeak for “I just found out.” Large-scale reform of the American health-care system is one of the most complicated policy issues the government faces, as all of Trump’s modern predecessors learned.

“The health care reform story illuminates almost every aspect of the presidency,” David Blumenthal and James Morone write in “The Heart of Power: Health and Politics in the Oval Office,” a 2009 examination of how eleven Presidents, from to Franklin Roosevelt to George W. Bush, grappled with the issue. “Because health reform is excruciatingly difficult to win, it tests presidents’ ideas, heart, luck, allies, and their skill at running the most complicated government machinery in the world.”

Those who were successful at pushing reform operated in extremely advantageous environments. Lyndon Johnson and Barack Obama, two Presidents who dramatically expanded coverage, were able to pass legislation largely because they had big majorities in Congress.

President Obama had an especially favorable terrain. His White House was filled with veterans from Capitol Hill. He was operating in the emergency environment of the Great Recession, which gave him more political capital. His own party was unusually united on the framework of reform, which had its roots in conservative think tanks and had already been tried in Massachusetts by a Republican governor. Even the Democratic left, which favored a single-payer system, quickly signed on to the Obama plan. Early on in the process, Obama cut deals with the major corporate interests—drug companies and the insurance industry—that previously had blocked reform. Most important, he had sixty Democratic votes in the Senate to block a filibuster. When his Senate majority slipped from sixty to fifty-nine, his legislation almost died.

The environment for reform under Trump is far more precarious. Trump’s White House is staffed with political neophytes, and the President himself is so inexperienced that he only yesterday determined that health care is a “complicated” issue. Unlike the Democrats in 2009, Republicans are divided. In the House, the most conservative members are rebelling against a core component of the leading plan being developed by Speaker Paul Ryan, who favors refundable tax credits to help Americans pay for insurance. Yesterday, the leaders of the two largest groups of conservatives, the Freedom Caucus and the Republican Study Committee, separately said that they will vote against reform bills that include tax credits, which they argue are tantamount to a new entitlement program.

In the Senate, there is no consensus among Republicans on a plan to replace Obama’s Affordable Care Act. For major parts of his effort, Trump can use the budget process known as reconciliation, which is not subject to a filibuster and which Obama used for a final vote on his plan after Senator Ted Kennedy died and was replaced by Republican Scott Brown. But Trump will still need sixty votes to complete an overhaul of the current system. There are currently only fifty-two Republican senators.

The White House staff is reportedly divided over the way forward, with Trump aide Jared Kushner and Gary Cohn, the head of National Economic Council, seen “as skeptics” of the House proposal, according to the Times. Reince Priebus, Trump’s chief of staff, and Tom Price, a former Republican congressman who is now Secretary of Health and Human Services, favor the Ryan approach.

Other important constituencies are also divided. The governors who met with Trump yesterday expressed an array of opinions about what he should do regarding the Medicaid expansion initiated by Obama. Under Obama, the insurance industry, which has frequently torpedoed reform, accepted new regulations, including a ban on denying coverage to new policyholders with preëxisting medical conditions, in exchange for the individual mandate, which required Americans to buy their products. Republicans want to keep the ban and get rid of the mandate, a deal that might be worse than the status quo for most insurers, without additional concessions.

The A.C.A. is more popular with the public than it has been since September, 2010, according to the Kaiser Health tracking poll. And during the recent congressional recess, many Republicans were faced with protests from constituents at town-hall meetings across the country. All of this has emboldened Democrats, especially those, like Senator Chuck Schumer, who have been around long enough to see health-care reform frustrate the ambitions of several Presidents.

“I predict the discord in their party will grow as Republicans return to Washington after this last week of angry town halls,” Schumer said in remarks at the National Press Club yesterday. “I believe the odds are very high we will keep the A.C.A. It will not be repealed.”

In their history of health-care reform, Blumenthal and Morone conclude with eight conditions necessary for passing major reform. The first, and perhaps most important, is “passion.”

“Major health care reform is virtually impossible, difficult to understand, swarming with interests, powered by money, and resonating with popular anxiety," they write. "The first key to success is a president who cares about it deeply.” Any President who is just learning the basic fact that health care is “complicated” has failed the passion test. And without that, little else matters.