House Speaker Nancy Pelosi on Thursday warned congressional Democrats who support impeachment proceedings against President Trump not to “disparage” colleagues who don't, a source familiar with the conversation told Fox News.

The stern guidance came during a morning meeting on Capitol Hill, on the heels of Robert Mueller's testimony which left pro-impeachment Democrats with little new material to pursue their case. The source told Fox News that Pelosi told lawmakers they are still allowed talk about impeachment if it's politically important for their home districts, but urged them not to malign members who aren't in the same camp.

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“She said, ‘Do what you have to do for your districts, but don’t disparage those who are not for it,’” the source said, recalling Pelosi’s remarks. “She said not to make it a thing about their patriotism or lack thereof if they are not for it.”

The source added that Pelosi even warned them not to “make it a thing” that members in support of impeachment proceedings are “following the Constitution” because it “implies that those of us who don’t support it are not following the Constitution.”

Pelosi, especially in recent weeks, has been trying to tamp down the infighting in the caucus between far-left and more moderate elements of the party. As part of that effort, she is set to meet with Rep. Alexandria Ocasio-Cortez, D-N.Y., on Friday -- the freshman lawmaker's chief of staff is among the Hill figures who've been antagonizing centrist Democrats.

But the impeachment question threatens to further divide the caucus after Mueller's testimony left the future of that push as unclear as ever. Pelosi, for her part, has resisted impeachment pressure from the start.

Mueller stood by his team’s findings at the hearings before both the House Judiciary and House Intelligence Committees—reiterating that the special counsel’s office had found no evidence of a criminal conspiracy between Trump associates and Russia, while also stating that the president was not exonerated on allegations of obstruction of justice despite his assertions to the contrary.

But in doing so, Mueller repeatedly refused to drift beyond the bounds of his report. He also declined to go down the road of the impeachment topic, under questioning from both Republicans and Democrats.

Rep. Veronica Escobar, D-Texas, of the Judiciary Committee, directly questioned Mueller on whether he was suggesting that Congress impeach Trump.

“You explained [in May] ... that the Constitution requires a process other than the criminal justice system to formally accuse a sitting president of wrongdoing,” Escobar said, quoting Mueller’s remarks during his press conference in May. “That process other than the criminal justice system to accuse a sitting president of wrongdoing—is that impeachment?”

“I’m not going to comment on that,” Mueller said, as she continued to press the issue, citing a footnote in the report.

“What are other constitutional processes?” she said.

Mueller replied: “I think I heard you mention at least one.”

“Impeachment, correct?” she pressed.

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“I’m not going to comment,” he said

In May, Mueller’s statement was taken by many on the left as a green light to intensify talks about impeachment proceedings, and to ramp up existing Trump-focused investigations.

But on Wednesday, even as Republican Rep. Mike Johnson of Louisiana attempted to get an answer from Mueller on impeachment, the former special counsel wouldn’t bite.

Johnson said Democrats “desperately wanted you today to tell them they should impeach the president.”

“The report does not recommend impeachment, does it?” he asked.

Mueller maintained that he was “not going to talk about recommendations,” and when asked again, he stated clearly that he was “not going to talk about that issue.”

Rank-and-file Democrats have been calling for impeachment for months, as several House committees lead Trump-focused investigations into his alleged obstruction of justice, his financial history and ties to foreign individuals.

“I think there is a broad consensus in our caucus,” Rep. David Cicilline, R.I., said Wednesday, suggesting that Pelosi will get on board, despite being cool to the idea and helping turn back a recent impeachment resolution on the floor. “I think ultimately the majority of our caucus wants to move forward with an impeachment inquiry.”

The source told Fox News on Thursday that Pelosi “may be softening” to the idea.

But on Wednesday, Pelosi signaled the nearly nine hours of Mueller testimony barely rose to her attention.

When asked if she had watched the hearing, Pelosi, D-Calif., said Wednesday, “Just a little bit,” adding that she only watched a few moments “because we’ve been so busy.”

Fox News' Henry Erlandson contributed to this report.