Whether to side with Sen. Elizabeth Warren and liberal activists on bringing back Glass-Steagall regulations on banks was a "political decision" for Hillary Clinton during the Democratic primary, according to an email leaked from her campaign chairman's account.

The email, illegally obtained from Clinton campaign chairman John Podesta's account and posted online Monday by WikiLeaks, shows the political calculations involved in forming Clinton's platform regarding Wall Street, and the role that Warren, the outspoken bank critic, played in that decision-making.

In an email chain circulated among Clinton campaign aides and advisers on Oct. 2, 2015, participants discussed a draft of an op-ed by Clinton on Wall Street reform and whether or not it should address Glass-Steagall, the Depression-era law that separated commercial and investment banks. Warren, Clinton's rival Sen. Bernie Sanders, and other prominent liberals have pushed to reinstate the law.

Mandy Grunwald, a communications adviser, cited an aide describing the question as a "political decision."

"I am still worried that we will antagonize and activate Elizabeth Warren by opposing a new Glass-Steagall. I worry about defending the banks in the debate," Grunwald wrote. The first Democratic debate was scheduled for within two weeks.

Clinton, Grunwald said, was leaning toward backing the new Glass-Steagall. That would be a notable reversal for Clinton, who has long been perceived as aligned with Wall Street and whose husband signed the legislation that repealed Glass-Steagall in 1999, a move since much-criticized on the Left.

"I understand that we face phoniness charges if we 'change' our position now — but we face political risks this way, too," Grunwald wrote. "I worry about Elizabeth deciding to endorse Bernie."

It appears that the campaign was in contact with Warren about the possibility of embracing the law, one of her pet issues. Gary Gensler, a former regulator under President Obama and chief financial officer to the campaign, replied in the email chain that he had twice spoken about Glass-Steagall with "EW," presumably a reference to Warren.

Ultimately, Clinton left Glass-Steagall out of her agenda. Instead, she argued that the financial crisis affected mostly institutions that did not combine investment and commercial banking, meaning that the repeal of Glass-Steagall was not to blame, and that her plans would go further in addressing the threats to financial stability.

In doing so, she stopped short of one of embracing one of the key policy planks sought by outside progressive groups and subjected herself to several criticisms about her financial reform plans from Sanders during the debates.

Other emails published by WikiLeaks demonstrate the influence that Warren had on the policy decisions made by the campaign.

For example, a June 2015 email shows the campaign rushing to finalize its platform on college affordability in response to a Warren speech.

Ahead of a scheduled speech by the Massachusetts senator on policies to subsidize tuitions, Clinton policy adviser Ann O'Leary warned that "it will get quite a lot of attention and while we can still say our plan is coming later, the pressure will continue to mount."