President Barack Obama laughs at a joke told by Prime Minister Lee Hsien Loong's toast of the president during a state dinner, Tuesday, Aug. 2, 2016, in Washington. AP Photo/Jacquelyn Martin Barack Obama strode to the stage at last month's Democratic National Convention in an unusual speaking slot.

He spoke in the primetime hour Wednesday night, a spot typically reserved for a vice-presidential nominee.

In 2000, for instance, former President Bill Clinton spoke on Monday night of then-Democratic nominee Al Gore's convention. Former President George W. Bush, deeply unpopular in his second term, didn't show up for then-Republican nominee John McCain's party in 2008.

Obama's speaking slot was by design. It previewed an outsize role in his final campaign: Electing Hillary Clinton to be his successor in the White House.

"President Obama gives Hillary Clinton a hat trick: He can help unite the party by bringing out Bernie Sanders supporters into her camp, deliver an aggressive contrast about the threat posed by Donald Trump, and ensure that all the supporters of the Obama coalition show up in November," Ben LaBolt, a former spokesman for Obama's presidential campaigns, told Business Insider earlier this year.

Obama is prepared to campaign for his party's presidential nominee more than any sitting president in recent history. That could be a big problem for the GOP and its nominee, Donald Trump. And a huge boon for Clinton.

The president's approval rating got its own convention bump: In a CNN/ORC poll conducted after the convention, 54% of Americans said they approved of Obama's job performance. It was his highest mark since right before his second inauguration in 2013. Just 45% disapproved.

That number is significant. Earlier this year, an NBC/Wall Street Journal poll found that President Barack Obama's approval rating had jumped to 51% — its highest point since his second inauguration.

NBC's team of political analysts called it the "most important number" out of the poll.

"Why is it important? Because it means that Obama will be an asset to Hillary Clinton on the campaign trail unlike he was in the 2014 midterms, when his approval rating was in the low 40s," NBC's Chuck Todd, Mark Murray, and Carrie Dann wrote.

The threshold might seem arbitrary. But historical precedent suggests it could bode well for Clinton, Obama's former secretary of state.

Early this year, Obama's approval rating hit 50% in the weekly average from Gallup's daily survey. As of Friday, it stands at 51%. For Obama, whose approval ratings have been stuck in the mid- to low-40% range for much of his second term, it was a notable bump.

"While it's hard to pinpoint precisely why Obama's approval rating has risen among Democrats recently, there are a number of plausible explanations," wrote Andrew Dugan, a Gallup analyst, and Frank Newport, the organization's editor-in-chief, in a post earlier this year.

One of the explanations, the pair concurred, was that "the unusual status of the Republican primary race — exemplified in particular by frontrunner Donald Trump's campaign style and rhetoric — may serve to make Obama look statesmanlike in comparison."

Donald Trump at a campaign rally in Florida. Mark Wallheiser/Getty Images

Trump has come into Obama's crosshairs repeatedly as he has hit the trail for Clinton. And with good reason: More so than at any other presidential hand-off in recent history, so many elements of the current administration's legacy are at stake.

The Republican nominee has pledged to undo signature achievements on healthcare (the Affordable Care Act), the environment (historic new regulations aimed at curbing climate change), and foreign policy (the Iran nuclear deal).

Those themes will become evident as the president launches into what will be his final campaign: Preventing a Trump presidency.

"Not only does he have strong standing among Democrats and independents, but he has a unique ability to mobilize the young voters and diverse communities she'll need to win," LaBolt said.

Obama's approval ratings at this point are far better than those of Bush, his predecessor, off whose unpopularity Obama thrived during his 2008 run. His level is most directly comparable to former President Ronald Reagan, who in March 1988 held a 51% approval rating, according to Gallup.

That same year, voters selected George H.W. Bush — Reagan's vice president — to succeed him.

"Yes," said Ari Fleischer, President George W. Bush's former press secretary, when asked earlier this year if Obama's apparent rising popularity poses a problem for the Republican Party.

"Certainly, going into an election spring and summer, it’s better to have an incumbent president increasingly popular rather than less popular if you’re the incumbent party," he told Business Insider.

The numbers present a striking contrast to some data points associated with the current Republican presidential frontrunner.

Barack Obama and Hillary Clinton at the Democratic National Convention. Alex Wong/Getty Images

A recent Gallup survey revealed that 42% of voters view Trump in a "highly unfavorable" light, compared with 16% who see him highly favorably. That's the highest negative percentage for any major presidential candidate since at least 1956, according to Gallup.

"I've been doing this [since] 1964, which is the Goldwater years," NBC/WSJ co-pollster Peter Hart told NBC of the relative unpopularity of many of the candidates earlier in the year. "To me, this is the low point. I've seen the disgust and the polarization. Never, never seen anything like this. They're not going up; they're going down."

Closest to Trump? Clinton, whom 33% of the electorate views highly unfavorably.

It helps explain why Clinton is attaching herself to much of Obama's legacy. And Obama remains favorable to wide swaths of constituencies that Clinton needs to turn out to vote in November. The president holds high approval ratings among African-Americans (90%), Democrats (82%), Latinos (73%), and voters aged 18 to 34 (64%), according to Gallup.

And despite the strong primary challenge from Sen. Bernie Sanders, in many ways, Clinton has run an incumbent-style campaign, and she has had much of the party's establishment rallying behind her candidacy.

As Gallup's Dugan and Newport wrote earlier this year:

"In comparison, the two most recent candidates running to succeed a two-term president of the same party — John McCain running to follow the unpopular Bush, and Al Gore trying to succeed the popular but scandal-prone Bill Clinton — went to greater pains to ensure they were not associated with the outgoing president."

They concluded: "Prior to that, George H.W. Bush in 1988 presented himself as a natural heir to the Reagan legacy and was able to win his own term."