Washington’s think tanks are morphing into powerful activist organizations, blurring a longtime distinction between academia and advocacy.

With Sen. Jim DeMint, R-S.C., taking the helm in April, The Heritage Foundation will have the look and feel of a shadow Republican Party equipped with a bustling political team and six registered lobbyists, a counterweight to the Democratic Center for American Progress.

Both think tanks are barred from politicking. They rely instead on politically active nonprofits, which are separate legal entities, to influence elections in favor of candidates who support their policies.

“Heritage over time, and CAP to the same degree, have really pushed the envelope in terms of 501(c)(3) status,” said James McGann, who studies think tanks at the University of Pennsylvania. “It not only puts in peril the institution but the entire think tank community because it blurs the line.”

“Historically, in terms of the IRS, think tanks have not had a problem,” he added.

But that may soon change as some institutions push their policy ideas aside and more outwardly embrace their party affiliations.

The Heritage Foundation set up its affiliate Heritage Action, a 501(c)(4), in September 2010, shortly after the Supreme Court’s ruling in Citizens United v. Federal Election Commission opened the door for tax-exempt groups to spend money freely in politics. It raised more than $4.5 million in 2011, tax documents show, and is on pace to match that in 2012, according to a Heritage official. The group, which has two field offices, aims to increase its presence in lawmakers’ districts in preparation for 2014, the official said.

“We wanted to have our ideas promoted just as aggressively as special interests were,” said Jim Weidman, a spokesman for the foundation, which raised almost $80 million in 2011.

An increasingly polarized climate in Washington has only greased the wheels. The think tanks are competing for donations with a new set of players such as Priorities USA Action, a Democratic super PAC, and the conservative grass-roots Americans for Prosperity, which says it raised more than $110 million this year.

“Now [think tanks] have to promote their ideas and explicitly tell the members ‘if you don’t pay attention to those ideas were not going to rate you very favorably,’” said former Republican Rep. David M. McIntosh of Indiana. “[DeMint] will have a great understanding of the potential that Heritage has to really make a difference with the changes in the law.”

While Heritage and CAP are the only think tanks that now field registered lobbyists and have advocacy arms, nearly all of the major research institutes in Washington have a team advocating their policies on Capitol Hill. As of September, CAP Action Fund spent nearly $200,000 on lobbying Congress and Heritage Action spent $120,000, Senate reports show.

“We don’t think it is enough to write about our ideas, we want to see them actually improve people’s lives,” said CAP President Neera Tanden, who served as a domestic policy director for President Barack Obama’s 2008 campaign.

The Heritage Foundation also uses congressional travel to promote its polices, focusing in particular on the House Republican Study Committee, the conservative wing of the Republican caucus.

A representative described a retreat last January in Philadelphia as “a 50,000-foot extended dissertation” on the organization’s principles. It cost Heritage more than $50,000 to send 40 members and a handful of staffers on the three-day visit to the City of Brotherly Love, where they attended panels and visited the Liberty Bell.

In 2011, Heritage spent almost $125,000 to fly about 50 lawmakers and a few staffers — along with spouses and other family members — to a Simi Valley, Calif., retreat at the Ronald Reagan Presidential Foundation and Library.

Though think tanks including the Brookings Institution, The Cato Institute and the Center for American Progress also sponsor congressional travel, Heritage’s expenditures far exceed the others.

Some worry that DeMint will make Heritage so overtly political that its scholars will be reluctant to tackle controversial policy issues if they run counter to the party line.

Bill Antholis, managing director at The Brookings Institution, said the shift narrows the field for scholars committed to bipartisan research.

“Many of us have seen this as an opportunity to capture the ground that cuts across both parties,” he said.

Earlier this year, scholars at the libertarian Cato Institute successfully fought off efforts by conservative philanthropists David and Charles Koch to seize control of the organization, arguing it would damage the institute’s reputation for independence.

Heritage, however, says outgoing President Edwin Feulner founded the institution with political activism in mind, after House Republicans lost a vote on an amendment he had championed. Just days later, policy scholars approached Feulner, then the executive director of the RSC, with a white paper supporting the measure. They had waited to release the report, the story goes, so they wouldn’t influence the vote. Soon, Heritage was born.

“Some people may knock us for not being think-tanky enough,” a Heritage official told CQ Roll Call on Dec. 7. “We’ve always been an activist think thank. That’s why we existed from the beginning.”

Amanda Becker contributed to this report.