In an age of partisan media, the lines between “partisan” and “media” can sometimes blur.

Case in point: The pool reporter covering Vice President Pence on Thursday — that is, the reporter who supplied details about Pence’s daily activities as proxy for the rest of the press corps — was an employee of the Heritage Foundation, the conservative think tank.

In other words, the news that reporters received about the vice president came from a journalist employed by an organization with a vested interest in the direction of White House and federal policy.

The development is unusual; the reporter, Fred Lucas, is the first member of his organization to take on pool reporting duties, which are typically handled on a rotating basis by mainstream news organizations. Lucas also covered Pence as the pooler two weeks ago.

Lucas writes for the Daily Signal, a news and commentary site started nearly three years ago by Heritage, one of Washington’s leading policy shops. The Signal covers issues that are a focus of Heritage’s conservative agenda, such as an Obamacare repeal, tax policy and illegal immigration.

Vice President Mike Pence. (J. Scott Applewhite/AP)

While there were no objections to Lucas’s pool reports on Pence, some journalists suggested the presence of the Signal as a member of the pool crossed a symbolic line, into greater legitimacy for the partisan press.

“The short answer is that it’s concerning that news organizations with a clear and stated bias are serving as the eyes and ears of the White House press corps, regardless of their political leaning,” said Andrew Seaman, a Reuters reporter who is chair of the Society of Professional Journalists’ ethics committee. “In a perfect world, only news organizations with editorial independence and proven track records of reliability should be able to provide pool reports for the White House or any other government agency or official.”

The White House press office provides credentials to reporters. The White House Correspondents’ Association, an organization of journalists, assembles the pool, so it was responsible for putting Lucas in the rotation.

Jeff Mason, the WHCA’s president, said his group would review the criteria for selecting members of the “supplemental” pool — the group of reporters who can supplement the regular pool when needed — but he declined to say whether the Daily Signal’s recent participation prompted the move.

The Daily Signal’s inclusion in the pool could set a precedent for other advocacy organizations, such as the liberal Center for American Progress, that have expanded into newsgathering. These groups could argue that they, too, qualify for White House press credentials and pool shifts. The slope could become even more slippery if extremist or racist organizations sought similar status.

The Signal’s editor, Rob Bluey, vigorously defended his organization’s presence in the pool, saying there’s “a hard firewall” between Heritage’s policy and lobbying operations and the Daily Signal’s newsroom.

Heritage’s leadership, including its president, former senator Jim DeMint (R-S.C.), has “never ordered us to cover any story” in the Daily Signal’s existence, Bluey said. “I wouldn’t work here, and the talented journalists we’ve attracted to work here wouldn’t be here, if we were receiving direct orders from Jim DeMint and the Heritage Foundation.”

Nevertheless, Bluey acknowledged that the Signal’s editorial independence has been questioned before, most prominently by the congressional Periodical Press Gallery, a journalist-run operation that credentials journalists to cover Congress.

Despite covering legislative issues, the Signal has been unable to secure press passes to cover Congress. The gallery’s rules prohibit granting passes to reporters who work for organizations whose parent companies are involved in advocacy or to publications that are not financially independent news organizations. The rule is designed to prevent lobbyists or other advocates from securing press accreditation.

However, the White House press office, which oversees credentialing, operates under a looser standard. It has historically, on First Amendment grounds, been reluctant to exclude many kinds of publications, which has led to news organizations from across the political spectrum gaining access.

Last month, for example, the White House granted press credentials to the Gateway Pundit, a blog that is supportive of President Trump and that has promoted dubious reports about Hillary Clinton’s health and the extent of voter fraud. White House press secretary Sean Spicer now regularly takes questions at daily briefings from pundits and talk-radio hosts via Skype.

The SPJ’s Seaman acknowledged that many news organizations are owned by large corporations with other interests and businesses. So “setting restrictions on press access by a parent company may open a proverbial can of worms,” he said.

In view of all this, Bluey said the Daily Signal handling of pool duties “isn’t really new territory.” He said there’s “a double standard” at work in Washington about determining what is and what is not a legitimate news organization.

“Who owns The Washington Post?” he asked rhetorically in reference to Jeffrey P. Bezos, The Post’s proprietor, who also is founder and chief executive of Amazon.com. “He doesn’t have an agenda, too?”

As a candidate last year, Trump accused Bezos of buying The Post in 2013 to advocate on behalf of Amazon on issues such as sales taxes and antitrust enforcement. He offered no evidence for his assertions.

The Post’s editorial board has consistently editorialized in favor of taxing online retailers such as Amazon. In response to Trump, Bezos said he welcomed scrutiny of Amazon’s tax structure and said Trump was acting in a way that was “not an appropriate way for a presidential candidate to behave.”

Correction: An earlier version of this article mischaracterized Mason’s description of the WHCA’s review of pool selection criteria. This version been corrected.