Washington — Unable or unwilling to completely erase his predecessor's signature initiatives, President Donald Trump this week turned to another approach: wreaking havoc.Trump's back-to-back body blows against President Barack Obama's health care law and nuclear agreement with Iran demonstrated the president's embrace of turmoil as strategy. In both cases, he plunged a pair of policies with broad domestic and international implications into a state of confusion and uncertainty, hoping that the disorder will force Congress to take action.Trump has long thrived on unpredictability, an attribute he views as a virtue. But to the lawmakers, foreign partners, businesses and consumers now sorting through the implications of his announcements this week, the strategy looks far less appealing.International allies who spent years negotiating the nuclear accord alongside the US are now left waiting to see if Congress will reinstate nuclear sanctions on Tehran, a move certain to jettison the deal. Trump didn't specifically ask for the sanctions to be put back in place. But, in a speech declaring he would no longer certify the deal, he did ask lawmakers to add new, unspecified conditions for US cooperation in the agreement.On health care, millions of Americans face the prospect of higher insurance premiums as a result of Trump's decision to immediately halt payments to insurance companies that provide lower-cost plans to low-income people. Trump calls the payments a bailout to insurance companies and he cited as justification a legal dispute over whether the payments were legally authorised. Trump yanked the money without any plan in place for offsetting cost increases for customers. Insurance companies, too, are at the mercy of lawmakers, who must now decide whether to restore the payments."We are going to have to figure out a way to stabilise the situation," said Rep. Charlie Dent, a Pennsylvania Republican who dubbed the move "ill-advised". Democrats branded it sabotage. The president was "determined to inject chaos and confusion" into the health care system, said Sen. Mark Warner, a Virginia Democrat.As a businessman, a candidate and now as president, Trump has gravitated toward chaos. His campaign was rife with bitter internal rivalries, often stoked by the man at the top of the ticket. His West Wing has careened from crisis to crisis and endured more staff upheaval in nine months than some presidents experience in a full term.Still, Trump has made clear he sees unpredictability as an advantage. Indeed, his vague statements — "we'll see," he often says when asked about looming decisions — and seemingly improvisational policy positions can leave his political rivals maddeningly frustrated. He's vowed to keep international adversaries off balance with diversionary tactics or a simple lack of transparency about US actions — a goal some foreign diplomats say he has indeed fulfilled.Trump's approach, however, hasn't yet translated into success when it comes to making good on his vows to overhaul some of the cornerstones of Obama's legacy, including the Iran deal and the health care law, that have long loomed as targets for Republicans. As a candidate, he promised to rip up the Iran deal on his first day in office. He boasted that overhauling health care would be "easy".Health care has proven to be anything but simple. Even with Republicans in charge on Capitol Hill, the GOP has been unable to muster the votes to muscle through an "Obamacare" replacement package. Lawmakers' impotence has deeply frustrated Trump and left him casting about for ways to undermine the law on his own.Thursday's announcement halting the subsidies for insurance companies marked Trump's most aggressive move yet to chip away at the law. Eliminating the payments would trigger a spike in premiums for some Americans next year, unless Trump reverses course or Congress authorizes the money, a step that would almost certainly require the kind of bipartisanship that has been absent on Capitol Hill this year.In a sign of the potential difficulties to come, Trump appeared to pre-emptively blame Democrats if no deal is reached, tweeting that they should "call me to fix!" And Democratic leaders made clear they would turn the blame-game back around on the president.House Minority Leader Nancy Pelosi said she wanted voters to know "what it means in their lives when he goes off on a spiteful, cruel toot to diminish their access to affordable care."Trump also has been angered by his struggle to roll back the Iran nuclear accord Obama vigorously championed. Amid warnings from his advisers about the risks of withdrawing from the accord, he ordered national security advisers to help him find a way to avoid having to certify Iran's compliance with the deal every 90 days.That plan, which Trump announced from the White House on Friday, still falls short of scrapping the agreement. Instead he asked Congress to toughen the law that governs U.S. participation and fix what he sees as deficiencies in the measure.Trump's half step followed weeks of pleas from allies who argue Trump cannot pull out of a deal that was negotiated alongside Britain, France, Germany, Russia and China. Federica Mogherini, the European Union's foreign policy chief, declared Friday: "The president of the United States has many powers. Not this one."For allies looking for reassurances that Trump was done threatening to withdraw from the Iran deal, he offered nothing but more uncertainty."We'll see what happens over the next short period of time," Trump said.- Julie Pace has covered the White House and politics for the AP since 2007. Follow her on Twitter.