Donald Trump is tearing America apart with his divisive policies as he races to destroy Barack Obama's legacy.

But the wilful President won't be able to take his wrecking ball to these five great triumphs.

Mr Obama has been painted as a disappointment by cynical observers and deflated Democrats, yet he has etched in stone landmark changes in education, healthcare, the economy, climate change and nuclear agreements.

Top US political commentator Jonathan Chait says that despite the criticism, the former commander-in-chief had some remarkable successes, which Mr Trump will not be able to simply run his Sharpie through.

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Here's why Mr Obama was no failure.

WHAT DID PRESIDENT OBAMA ACHIEVE?
"There's his economic record - fiscal stimulus, bank rescue, auto bailout," said Chait, author of new book Audacity on the former commander-in-chief. "The Affordable Care Act went through legislation.

A photo of former President Obama is held up during a Central Florida Women's Rally. Photo / AP
A photo of former President Obama is held up during a Central Florida Women's Rally. Photo / AP

"There's climate change - wind and solar power are much more prevalent, he produced international agreements."

Mr Obama also negotiated an unprecedented nuclear deal with Iran, and Chait believes his greatest achievement was launching a massive overhaul of the education system, which he rarely spoke about for political reasons.

None of this will be easy to remove.

The Republicans are already having "incredible trouble" launching an effective attack on their number one target, Obamacare, and keep pushing back the problem. "They're afraid to tear this up," said Chait. "Markets unravel, tens of millions of people lose healthcare. They have no idea what to put in its place."

If Mr Trump pulls out of the Paris Agreement on climate change, as he has vowed to do, Chait says that will signal a halt to progress, rather than a backwards step. "I don't see any possibility we could go back to 2009, where coal was bigger and energy efficient devices were less in use," he said. "The green energy revolution isn't going away, but it will slow down. And that could be a catastrophe for the world, because it needs to speed up."


'MOST POPULAR PRESIDENT IN HISTORY'
The 55-year-old has made it out of his eight-year tenure with his youth and reputation intact, something virtually none of his tarnished predecessors have managed. And while he had spoken of lying low for a while, he recognised the need to speak out against the new President's controversial travel ban.

Many have denigrated Mr Obama's biggest achievement as simply what he represented for race relations as the first black president of the US, but Chait believes he sketched out a progressive vision for racial progress, despite the conflicts.

"He's the most popular outgoing president in US history, yet his successor is attempting to roll back his policies," said the Washington-based New York magazine columnist.

President Donald Trump speaks at the Republican congressional retreat in Philadelphia. Photo / AP
President Donald Trump speaks at the Republican congressional retreat in Philadelphia. Photo / AP

"People frame this the wrong way, as rolling back Obama's legacy. The legacy he's rolling back would be of all 44 presidents."

Chait says it is simply a shortsighted view and the smokescreen of extremist propaganda that conceal enormous evidence of Mr Obama's enduring accomplishments.

He says the former president's key role now will be to train the Democratic leaders of the next generation.

"There's a lack of appreciation for Obama and what he did, but people like him, they have sympathy for him and they admire him," said Chait.

"There's every reason to promote his role in the Opposition, and I think he'll take that."

WHAT WILL TRUMP DO NEXT?
The former president has been accused of relying on executive orders to sign off policy he couldn't get past a hostile Congress, meaning Trump can now easily undo his achievements with further orders.

Chait says this is inaccurate. "The notion Obama relied mostly on executive orders is a myth," he said. "I was surprised to hear the retort Trump would roll back executive orders. The vast majority of Obama's legacy actually had deep support and reach."

But there is reason to be nervous. Trump craves approval, and has complained bitterly about the protests against him. If the 70-year-old cannot persuade people to agree with his policies, he may force them.

"I worry about authoritarianism," said Chait. "I see little evidence Trump has any popular basis for his policies. He is extraordinarily unpopular at this early stage, his approval rating is extraordinarily bad. He benefited from serious fluke circumstances and an unpopular opponent. I don't see him building support."

The former reality star is likely to blame his staff if his difficulties continue, and has already fired his attorney general for her "betrayal" over his Muslim ban.

President Donald Trump has been busy signing executive orders. Photo / AP
President Donald Trump has been busy signing executive orders. Photo / AP

The Democrats now have a great chance. The Left had become mired in complacency during a long spell in power, but Trump's actions and statements have "awakened the liberal base in the US in a way never seen before", says Chait. The Republican party will be afraid of a backlash in the midterm elections.

"At some point, they're going to need to turn on Trump as a matter of political survival," he added. "If opposition grows, it will force the Republicans to make Congress a separate branch as designed by the constitution to hold the president to account."