Donald Trump’s decision to go it alone with rapid fire announcements on healthcare and Iran reflects his boiling frustration with the limits of presidential power, analysts say.

The US president made a brazen move on Thursday night to halt payments to insurers under Barack Obama’s healthcare law. Democrats accused him of a “temper tantrum” and spiteful attempt to sabotage legislation he promised but failed to replace. Less than 24 hours later, he condemned the “fanatical” government of Iran as he decertified his predecessor’s nuclear deal, defying his own cabinet and disquieting European allies.

The one-two punch showed Trump straining to assail Obama’s legacy but stopping short of terminating either the Affordable Care Act, known as Obamacare, or the Iran nuclear accord. Both are back in the hands of Congress, a source of constant exasperation for the property tycoon turned novice politician, who finds himself isolated and lashing out.

“The Congress has been frustrating to him,” John Kelly, the White House chief of staff, told reporters on Thursday. “Of course, our government is designed to be slow, and it is. His sense, I think, as a man who is outside the Washington arena, a businessman, much more of a man of action, I would say his great frustration is the process that he now finds himself [in].

“Because, in his view, the solutions are obvious, whether it’s tax cuts and tax reform, healthcare, infrastructure programmes, strengthening our military. To him, these all seem like obvious things that need to be done to protect the American people, bring jobs back.”

Since taking office 10 months ago as the first US president with no previous political or military experience, Trump has been given a crash course in the workings of government and the delicate balance of power between the White House, Capitol Hill and the courts. That his writ only runs so far has come as a rude awakening. His executive orders can only achieve so much, and frustrations have sometimes spilled out in impetuous speeches and tweets.

Rick Tyler, a political analyst and partner at Foundry Strategies, said: “He is acutely aware of the limits of presidential power. It’s not like being the CEO of a company where you just do what you want to do.

“By using executive orders, Trump is making something happen on healthcare. He’s prevented from changing it himself, but will force another branch of power to react. It’s the same on Iran.”

Having repeatedly vented his anger at the Republican-controlled Senate for failing to repeal and replace Obamacare, despite seven years of promises, Trump has now thrown a spanner in the works by ending the so-called cost-sharing subsidies that help people on low incomes. The White House claims the government cannot legally continue to pay the subsidies because it lacks formal authorisation by Congress.

Donald Trump has responded by his inability to govern as he likes by throwing red meat to his base. Photograph: Yuri Gripas/Reuters

The president explained on Friday: “It’s step by step by step and that was a very big step yesterday … We’re going to have great healthcare in our country. We’re taking a little different route than we had hoped, because Congress forgot what their pledges were. So we’re going a little different route. But you know what? In the end, it’s going to be just as effective, and maybe it will even be better.”

The intervention, however, could backfire. It was condemned by Democrats including the House minority leader, Nancy Pelosi, who told reporters: “The president single-handedly decided to raise America’s health premiums for no reason other than spite and cruelty.” Senator Chris Murphy tweeted: “Trump’s decision to stop ACA payments is nuclear grade bananas, a temper tantrum that sets the entire health system on fire. My god.”

Doctors’ groups also warned of “dramatic, if not catastrophic, increases in premiums across the country” and millions of Americans losing coverage. Nineteen states plan to sue.

Trump has previously blamed the lack of healthcare fixes on Obama or Congress, but he now risks being held personally responsible for cutting the system off at the knees. Robert Shrum, a Democratic consultant, said: “The healthcare thing is madness in both policy and politics. He’s wilful, he’s angry, he’s clearly lashing out. He was better off leaving healthcare to Lamar Alexander and Patty Murray”, the senators working on a bipartisan deal.

Trump’s decision to stop ACA payments is nuclear grade bananas ... that sets the entire health system on fire. My god Senator Chris Murphy

Trump’s claim that Iran has not lived up to the spirit of the nuclear deal and his threat to terminate it also put him at odds with his secretary of state, Rex Tillerson, and his defence secretary, Jim Mattis. The Israeli prime minister, Benjamin Netanyahu, said he welcomed what he called a courageous decision, but the leaders of Britain, France and Germany said they stood committed to the agreement.

Evan McMullin, a former CIA operative and independent presidential candidate, wrote via email: “I think the president’s actions on healthcare and Iran are the latest examples of his standing political strategy, which is to throw red meat to his base in order to maintain his base, as evidence of his unfitness and inability to govern mounts.

“If anything, his use of this tactic seems to be accelerating as it becomes increasingly clear, even to some of his closest friends and political allies, that he is failing.”

This acceleration coincides with reports of a darkening in Trump’s mood. A report in Vanity Fair magazine, citing two sources, claimed he had vented to his longtime security chief, Keith Schiller: “I hate everyone in the White House! There are a few exceptions, but I hate them!”

The journalist Gabriel Sherman also wrote that several people close to the president told him that Trump was unstable, “losing a step” and unraveling. Such concerns appear to be reaching a critical mass. NBC News reported that Tillerson had referred to Trump as a moron. The president insisted the story was false, but challenged Tillerson to an IQ contest.

Senator Bob Corker set off a political firestorm when he responded to tweeted attacks by Trump. Photograph: Shawn Thew/EPA

Then Senator Bob Corker became one of the few Republicans on Capitol Hill to openly denounce Trump, though it is widely suspected that he speaks for many colleagues. During a Twitter clash last Sunday, Corker wrote: “It’s a shame the White House has become an adult day care center. Someone obviously missed their shift this morning.”

In an interview with the New York Times, the senator from Tennessee said: “I know for a fact that every single day at the White House, it’s a situation of trying to contain him … He doesn’t realise that we could be heading towards world war three with the kind of comments that he’s making.”

He also told the Washington Post on Friday that Trump had “castrated” Tillerson with remarks about his attempts to talk to North Korea.

Thomas Barrack Jr, a billionaire who was the top fundraiser for Trump’s election campaign, said he has been shocked and stunned by some of the president’s incendiary rhetoric and tweets.

“He thinks he has to be loyal to his base,” Barrack told the Washington Post. “I keep on saying, ‘But who is your base? You don’t have a natural base. Your base now is the world and America, so you have all these constituencies; show them who you really are.’ In my opinion, he’s better than this.”

If anyone can get through to Trump, it may be Barrack, one of his oldest friends. Rich Galen, a Republican strategist, said: “That got everybody’s attention because he’s a buddy and spoke at the Republican convention. So there seems to be some change. That’s part of what’s feeding it.”

McMullin agreed that Trump seemed rattled by the recent criticisms from Tillerson, Corker and Barrack. “He probably understands their remarks represent a new stage of acceptance setting in across the country, even among his supporters, that he is unfit and incapable.

“That, I think, is inspiring his accelerated efforts to throw red meat to his base to shore up their support. I expect that to continue, if not intensify, and to result in increasing political challenges for the GOP as 2017 and 2018 elections approach and in years to come.”