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Something we haven’t seen since 1988: A popular president hitting the trail for his successor

President Obama speaks during a campaign event in support of Democratic presidential nominee Hillary Clinton in Philadelphia last month. (Reuters/Carlos Barria)

George W. Bush didn't actively campaign for Republican presidential nominee John McCain in 2008 because, after years of war and scandal, Bush's approval rating was in the gutter. McCain got blown out.

Bill Clinton didn't actively campaign for Democratic nominee Al Gore in 2000 because, after years of questions about the Clinton's ethics, Gore wanted to distance himself from his onetime running mate. Gore lost the electoral vote by a fraction.

Ronald Reagan actively campaigned for Republican nominee George H.W. Bush in 1988, fundraising and attending campaign events for his vice president. Bush won.

At the time, Reagan's approval was a tick above 50 percent, ranging in the low-50s in Gallup polling as Election Day approached. There's a clear correlation between the approval rating of a president's job performance and how his party fares in the presidential election, as we noted last month when Post-ABC polling had President Obama's approval rating at 58 percent. The closer we get to Election Day, the tighter the correlation.

In January 2015, Alan Abramowitz of Sabato's Crystal Ball figured that an Obama approval rating of 55 percent would translate into a Democratic vote share in the 2016 election of 51 percent — certainly enough to retain the White House. That was before Donald Trump and before Hillary Clinton-vs.-Bernie Sanders, but the broader point stands: A popular Obama, by himself, is a boon to the Democratic presidential nominee's candidacy.

On Thursday morning, CNN released a new poll with its partners at ORC. Obama's approval rating now? Fifty-five percent, according to their numbers, up from 51 percent last month and up among a slew of important demographic groups.

What's an “important” demographic group? Well, for Clinton's candidacy it's some of those in the middle, shown in bolder text. Clinton needs to keep younger voters enthusiastic about having a Democrat in the White House. She needs to keep even with independents. And she needs to continue to convince women and white college graduates that their fears about her Republican rival are well-founded, prompting them to either defect to the Democratic Party (if not already there) or to not vote for Trump.

Some subset of women and white college graduates who are “meh” about Clinton view Obama more positively. In the most recent Post-ABC poll, 30 percent of those who viewed Clinton unfavorably nonetheless approved of Obama's job performance. Among college graduates, the figure was 39 percent.

Clinton debate prep is focused on what happens once the debate is done

That's where having Obama on the campaign trail can help. Obama is a very good campaigner — as is first lady Michelle Obama, whose own popularity is higher than her husband's — and can effectively help the Clinton campaign energize Clinton's base of support and push them to the polls. Obama has a job, of course, but he's been on the trail with some regularity and plans to make more campaign stops over the last 30-some days of the campaign.

There's also a quieter benefit to a popular Obama's stumping for Clinton: It's a subtle reminder that the living Republican presidents do not see Trump as qualified for the position. Trump and his supporters see the lack of support from the establishment as beneficial. For longtime Republican voters who are wavering on Trump, though, seeing Obama advocating so forcefully for Clinton may bring home the point that Republican candidates they have supported in the past refuse to do the same for the party's nominee this time.

There's very little downside to having a popular Obama on the campaign trail. Trump supporters hate him, but they are already Trump supporters anyway. Republicans are iffy on him, too, but those are not really votes that Clinton hopes to earn. A popular president is always helpful to his party. A popular president actually campaigning is something we have not seen in a while. But the last time we did, it worked out just fine for the president's successor.