From left, John D. Podesta, founder of the Center for American Progress; Neera Tanden, the group’s president; and former secretary of state Hillary Clinton at CAP’s 10th anniversary policy forum in Washington in 2013. (Yuri Gripas/Reuters)

It was early June 2015, and the political world was bracing for the Supreme Court to hand down a ruling on a key aspect of the Affordable Care Act.

Neera Tanden, president of the liberal think tank Center for American Progress, emailed top Hillary Clinton campaign officials with an idea about how to influence the decision: have the candidate and activists start talking about making the court an election issue so that the justices would understand the “political consequences” at stake.

“At CAP Action, we can get that story started,” she offered, referring to the group’s political advocacy arm. “But kinda rests on you guys to make it stick. What do you think? If you want to proceed, we should move soon.”

The episode, detailed in hacked emails posted by WikiLeaks, spotlights how CAP officials have played prominent behind-the-scenes roles assisting Clinton’s campaign since the former secretary of state launched her 2016 run. While Tanden, a former Clinton aide, is a well-known surrogate and adviser to the candidate, the emails show that she also offered the resources of her organization as she helped stamp out political fires and shape the debate around issues.

And her input was usually well-received, the emails suggest.

The Post’s John Wagner breaks down some of the consequences of the release by WikiLeaks of hacked emails from Hillary Clinton’s campaign. (Bastien Inzaurralde/The Washington Post)

“Not sure how in depth you are suggesting but seems like this should be manageable,” Jennifer Palmieri, Clinton’s communications director and a former CAP Action president, wrote in response to Tanden’s idea about the court, adding that the candidate had already been hammering on the election stakes for the Supreme Court.

In an interview, Tanden said that she advises the campaign in her personal capacity and that CAP Action weighed in only to promote a liberal policy agenda. She noted that she uses a personal email address to communicate with Clinton staffers, usually after hours.

“CAP Action can work with campaigns to push progressive ideas,” Tanden said.

The cache of correspondence offers a look at how CAP, which can accept unlimited donations and does not have to reveal the names of its contributors, would serve as a dominant idea factory and outside war room for a Clinton White House — potentially even more than it has for President Obama.

Much of Clinton’s current political brain trust is connected to the group, including John D. Podesta, who was White House chief of staff under former president Bill Clinton and now serves as her unpaid campaign chairman. Podesta founded CAP in 2003 as a response to GOP powerhouse think tanks such as the Heritage Foundation. While he has no daily oversight role now, he still serves on the board, and he regularly discussed campaign strategy with Tanden, the emails show.

In mid-February 2016, as the Democratic primaries were underway, Podesta wrote to Tanden suggesting edits to an op-ed she had written “on Hillary and family friendly policy.” Among his suggestions: that Tanden add the line, “I know people don’t feel like they really know what’s in Hillary’s heart; well, this is what I know.”

The Clinton campaign has refused to confirm the authenticity of any of the emails posted by WikiLeaks, but campaign officials have noted that government officials are investigating whether Russian intelligence services are behind the hack. The Obama administration has already officially accused Russia of attempting to interfere in the U.S. election, including through a previous hack into the computers of the Democratic National Committee.

Campaign officials declined to comment on how Podesta balances his positions at the campaign and CAP, but an official noted that he plays no role in CAP’s day-to-day activities, has no staff and does not receive any payment from the group.

CAP, which is set up under section 501(c)(3) of the tax code, cannot engage in political activity. But its sister advocacy group, CAP Action, which is a 501(c)(4), can do a limited amount of political work and communicate with the campaign — as long as the campaign is not directing its activities, legal experts said.

Kenneth Gross, a former associate general counsel at the Federal Election Commission, said that independent groups have leeway to interact with candidates and campaigns, but they cannot use information from those discussions in a paid advertising campaign or provide in-kind services such as polling.

Tanden said that CAP Action did not take sides in the Democratic primaries and engaged with all the campaigns on policy issues.

If Clinton “becomes president and the ideas that we put forward get adopted, that would be a great sign of our influence,” she added. “I think that CAP’s whole role from the beginning, and it’s part of our mission, has been to shift the debate in a more progressive direction.”

Still, the leaked emails show that Tanden was a central player in Clinton’s second presidential run from the early planning stages. She was among the invitees to a small November 2014 meeting at the former secretary of state’s personal office in New York to discuss policy proposals, including the possibility of offering a “significant middle-class tax cut.”

Among the questions on the agenda for the meeting: “Are there a few bold policy proposals that could . . . serve as signature pillars of a future progressive agenda?”

Other invitees included Podesta, longtime Clinton aide Cheryl Mills, senior policy adviser Ann O’Leary, economist Gene Sperling and former State Department adviser Tom Nides.

In January 2015, Tanden emailed Podesta to express concern about the makeup of Clinton’s campaign team.

“I’m not the diversity police but there is grumbling on the 4 white boys running the next presidential cycle,” she wrote. “So I recommend rolling out some people who look like the rest of America soon!”

CAP was also home to supporters of Sen. Bernie Sanders of Vermont, including senior fellow Lawrence Korb, who advised him on foreign policy. And CAP Action’s blog, ThinkProgress, published numerous flattering pieces about Sanders as his campaign gained steam.

But the emails show that Clinton had influential allies in Tanden and other top CAP officials.

After Clinton launched her bid, Tanden emailed the candidate directly with ideas on how to address rising economic populism. She back-channeled political intelligence to Podesta, including the fact that former New York mayor Michael Bloomberg would be interested in being secretary of state in a Clinton administration.

She also regularly sought to help quell controversies, including in July 2015, when she wrote to Podesta under the subject line “assistance.”

“let me know if there’s anything I or we [thru c4?] can do to help,” Tanden wrote about an unidentified media furor, adding: “I won’t do anything unless you tell me it helps.”

A month later, she offered suggestions on how Clinton should handle the controversy over her use of a private email server.

“Why doesn’t she just turn the server over to a third party at this point?” Tanden wrote. “Isn’t it going to leak out of the FBI anyway?”

“Done so think about something else,” Podesta replied.

In early 2016, three days before the Illinois Democratic primary, Tanden brainstormed how to get President Obama to indicate support for his former secretary of state.

“Can Obama even hint of support of Hillary before Tuesday?” she asked Podesta, who had served as a top Obama adviser. “Really, just a directional nod would be helpful. Like if he just asked a question or tweets an innuendo — how did he vote in the primary?”

Podesta responded: “Why don’t you push Valerie a little bit,” a reference to Valerie Jarrett, a senior adviser to Obama.

Clinton also got a boost from Judd Legum, the editor of ThinkProgress, who emailed Podesta several times with tips, using his personal email account.

“Not enough people were paying attention to your tweet that mentioned climate change,” Legum wrote to Podesta in April 2015, “. . . so I wrote a post about it. Looks like it’s going to be popular.”

He passed along a story titled, “This is The Most Important Tweet About Hillary’s Announcement And Everyone Pretty Much Ignored It.”

In February 2016, he emailed Podesta with the subject line “Major error by Bernie.” Legum noted that Sanders had said he had never tried to use his gender to rally support.

“Needless to say, he doesn’t say that because he doesn’t have to,” Legum added.

A month later came another flag from Legum to Podesta with the subject line “potential opportunity.” He shared a breaking story on ThinkProgress about an incident in which Trump’s campaign manager, Corey Lewandowski, had physically yanked a reporter. “Could be an opportunity for HRC to weigh in on Twitter, think it would go over well online,” he wrote.

Legum, who at one time was Podesta’s research assistant and was a Clinton campaign staffer in 2008, said that he was careful not to let his personal history shape ThinkProgress’s coverage.

“The correspondence between me and Podesta simply reflects me giving him advice in my personal capacity, in private,” he said. “The advice was not a reflection of ThinkProgress’s editorial approach to the campaign or candidates.”

Katie Zezima contributed to this report.