Left-leaning think tank Center for American Progress is fighting off an accusation that its chief operating officer blurred the lines between its policy research wing and its political wing in an email sent to staff following Democratic election victories Tuesday night.

The organization, known as CAP, is a nonprofit that is legally barred from supporting any political candidates or parties in order to keep its tax-exempt status. However, COO Gordon Gray celebrated helping to elect Democrats in a note to members of the research wing and the political wing, called CAP Action.

"Whether you are relieved, elated, or both, last night's election results show that we are on the right path and that CAP's efforts are paying off," Gray wrote in the missive to all staff Wednesday after Democrats won gubernatorial races in Virginia and New Jersey.

"Thanks to everyone who has been working so diligently (including over the weekend) on pointing out the truth about the proposed tax cut legislation," Gray continued, attaching the group's talking points on the House Republican tax plan. "It's another great example of cross-team collaboration at its best."

CAP is "an independent nonpartisan educational institute under section 501(c)(3) of the Internal Revenue code," per its website.

According to Cornell Law School, a 501(c)(3) organization should "not participate in, or intervene in (including the publishing or distributing of statements), any political campaign on behalf of (or in opposition to) any candidate for public office" to retain its tax-exempt status.

CAP itself stipulates online it "does not support or oppose candidates or political parties."

But CAP has a "sister organization," CAP Action, "an independent, nonpartisan policy institute and advocacy organization under section 501(c)(4)," which means it "must not be organized for profit and must be operated exclusively to promote social welfare."

The phrase in the email — "CAP's efforts are paying off" — prompted a group called CAP Whistleblowers, a network of "current and former CAP employees dedicated to blowing the whistle on hypocrisy and mismanagement at CAP," to send screenshots of the email to the Washington Examiner Thursday.

A current CAP employee who received the email, and is troubled by it, said it's clear the nonprofit, tax-exempt entity is violating its non-political status.

"Everyone who works here knows that CAP is a wholly-owned subsidiary of the Clinton Democratic establishment. We’re supposed to be a progressive place but our president spends all her time on Twitter picking fights with progressives and our new COO who was brought in to fix the place celebrates Democrats winning elections like that’s our job," the employee told the Washington Examiner.

"We all have to live with that and it’s embarrassing. There are no people [who] represent the progressive wing in any position of power — it’s all a bunch of Clinton burnouts who barely even bother to conceal their biases and act like our job is to elect establishment Democrats."

A spokeswoman for CAP told the Washington Examiner Thursday the email from Gordon was a reference to CAP Action, the group filed as a 501(c)(4) entity that's allowed to engage in political activity.

"Gordon's note was a shorthand reference to CAP Action’s election-focused policy work. Center for American Progress – the 501(c)(3) – did not and does not participate or intervene in any election," the spokeswoman said.

"Nowhere in that email does it imply that our job is to elect ANY type of candidates. But the job of the CAP Action is to do policy analysis and critique policies that are harmful to the American people and take on those who seek to erase any progressive policy gains made.”

Gordon joined CAP in September after serving as the executive vice president of the U.S.-Arab Chamber of Commerce.