New York, United States - Back in 2004, Barack Obama, then a fresh-faced senate wannabe from Illinois, burst onto the political scene with a rousing speech stressing national unity in the face of racial tensions and a controversial war in Iraq at a big party meet in Boston.

It was not the only time he worked a crowd to standing ovation. Obama is doubtless a great speaker whose blend of charisma, humility and infectious optimism can, on occasion, cause goose bumps and lumps in listeners' throats.

Observers are divided on the Democrat's best moment. Some point to his talk on military morality when accepting his Nobel Peace Prize, others cite his a cappella rendition of Amazing Grace after a white racist butchered a black church congregation in Charleston.

He will take the podium for the last time as United States president in Chicago on Tuesday night, in a speech to cement his legacy before his successor, Donald Trump, a Republican, takes office on a platform of dismantling much of Obama's work.

The billionaire realtor threatens to overturn Obama's healthcare finance policy, known as Obamacare, a painstakingly brokered deal to halt Iran's nuclear programme and a detente with the Cuban leadership.

Dismantling Obama's legacy

A backslide has already begun. Obama has until January 20 to clear out his desk in the Oval Office, but Republicans in Congress are already working on repealing his signature healthcare policy, the 2010 Affordable Care Act.

The scheme extended healthcare coverage to some 20 million people, but has been hit by soaring premium costs and major insurers pulling out. Obama has challenged Republicans to come up with a better alternative.

READ MORE: Barack Obama vows to save Obamacare

Don McCanne, a California-based doctor and fellow with think-tank Physicians for a National Health Program, said healthcare policy became a political football in an acrimonious fight that gridlocked Washington.

"It must be painful for Obama to watch Republicans start tearing up the universal healthcare policies that bear his name. He sincerely wanted to provide affordable care to all Americans, and made big political compromises on how this was achieved," McCanne told Al Jazeera.

"Of course, the end result was flawed. Republicans and Democrats are only tweaking at the system, not tackling the dysfunctional, fragmented finance structure that results in profound administrative waste, cost overruns and weak insurance products."

Obama's sing-song in Charleston was just one of many mass-shootings after which he played

"comforter-in-chief" to the bereaved. But, as with healthcare, the energised Republican right fought doggedly against new gun control measures.

Away from racial controversies

On Obama's watch, the growing prevalence of smartphone cameras saw US police officers being increasingly filmed using extreme, even deadly, force against black civilians, spurring the Black Lives Matter movement.

The police shooting of Michael Brown, an unarmed black teen, sparked riots in Ferguson, Missouri, and became a clarion call for a group that was ultimately left disappointed by an African American president who steered away from racial controversies.

"It felt like the winds of history were in our sails. We thought we were entering a new era, but Obama's government was largely unresponsive to the protests sparked by police killings of black people," Khury Petersen-Smith, a Boston-based Black Lives Matter activist, told Al Jazeera.

"He did not attend a single funeral of these murder victims. When racism came up, Obama deflected. He chose the side of the powerful, even as a movement of young black people raised the modest demand of stopping state violence against us."

READ MORE: Obama urges calm over black teenager's death

Global standing

Obama also has a mixed record overseas. He came to office in 2009 on pledges of "hope", "change" and repairing the US' alliances and tarnished global reputation after the divisive tenure of President George W Bush.

He promised to pull US forces out of Afghanistan and Iraq and to shutter the Guantanamo Bay base.

Eight years on, Obama has had to settle for scaled-back deployments to those Muslim-majority countries, while the Caribbean prison remains open, albeit with a smaller population of suspects in orange jumpsuits.

"Obama leaves the US in a much better state than when he took office, though Bush had set the bar very low. We can disagree with Obama's policies, but polls show improved US standing in the world," Jonathan Cristol, a fellow at the World Policy Institute, a think-tank, told Al Jazeera.

"Obama provided a virtually scandal-free administration run by a man of good character, with a family of role-models for the country and the world - something we will not get with Trump's incoming administration," Cristol said.

In his inaugural address, Obama told the US' foes that he would "extend a hand" of friendship. This outreach yielded a watershed pact with Iran, in which Washington lifted economic, oil and trade curbs in exchange for limits on its nuclear programme.

Restoring diplomatic ties with Cuba has resulted in stronger economic relations and a US embassy in Havana. Last year's global climate change deal commits nations to reducing the greenhouse gas emissions blamed for droughts and rising temperatures and sea levels.

WATCH: Barack Obama's legacy

'Passive foreign policy'

But Obama's successes may not last long into Trump's administration. While Obama spoke cautiously about the limits of American power, critics accuse him of subverting the US role as a global policeman.

The Arab Spring, in 2011, took the Obama administration by surprise. It initially supported protesters' calls for freedom, but pivoted back to its autocratic allies after Egypt's military coup and a Shia rebellion in Yemen.

After Washington accused Beijing of a land grab in the South China Sea, Obama did little more than object. He often looked outplayed by Vladimir Putin, as the Russian president backed rebels in eastern Ukraine and annexed the Crimean peninsula in 2014.

Obama is most frequently criticised for not enforcing his own "red line" against the Syrian president, Bashar al-Assad, after his government used chemical weapons on civilians in the country's brutal civil war.

Obama backed down from his threat to respond with force. His claim that Assad's "days are numbered" rang hollow as, backed by Moscow and Tehran, the despot slowly turned around a war that has claimed some 400,000 lives.

When addressing the UN General Assembly in September, Obama spoke of "constraints" on US power and "cooperation" between states. This sounded naive to realpolitik diplomats such as Henry Kissinger, who derided his "reactive and passive foreign policy".

OPINION: The troubling legacy of Obama's drone campaign

Broadly, more than half of those polled last year across parts of Europe, the Asia-Pacific and North America gave Obama the thumbs-up, according to Pew Research Center. His job approval rating of about 54 percent among Americans is favourable.

Not everyone agrees. At a debate hosted by Intelligence Squared US late last year, a crowd in liberal-leaning New York City voted for the motion that, on balance, Obama's foreign policy had been a failure.

"By temperament and intellect, Obama's just not equipped to guide American foreign policy in a world that's become suddenly rather dangerous," Michael Mandelbaum, a scholar and author of Mission Failure: America and the World in the Post-Cold War Era, told Al Jazeera.

"The strength of US foreign policy depends on unity in carrying out that policy of the American people. Obama has left the country, if anything, more divided than he found it. His promise at the 2004 Democratic convention to bring us all together didn't happen."

Others criticise Obama for not doing enough to tame the US' interventionist reflexes.

Although he scored a public relations victory by deploying the Navy Seals who killed al-Qaeda boss Osama bin Laden at his compound in Pakistan in 2011, a covert programme of drone strikes on suspected "terrorists" remains controversial.

"Obama's record contradicts the notion that he has pursued a policy of retrenchment," Michael Brenner, a scholar and former consultant to the US State Department and the Pentagon, told Al Jazeera.

"He's done absolutely nothing to diminish the presence of US military bases in the Middle East. He kept this archipelago of naval and air bases and supply bases throughout the Gulf, just like his predecessors."

Follow James Reinl on Twitter: @jamesreinl