WASHINGTON — Speaker Nancy Pelosi likes to talk about the numbers to defend her go-slow approach to launching a formal impeachment process against President Donald Trump.

"I think it's like 35 of them out of 238, maybe its 38 out of 238, have said they wanted to be outspoken on impeachment and many of them are reflecting their views as well as those of their constituents," Pelosi said at a Commonwealth Club of California Wednesday. "Yes, there are some, and the press makes more of a fuss about the 38 than the 200."

But there are strong signs that the pro-impeachment forces in the House are both larger than she portrays — and growing. That is, there's a lot of iceberg under the surface.

Since special counsel Robert Mueller spoke publicly for the first time about his finding that he could not exonerate the president on Wednesday, delivered shortly before Pelosi spoke, the number of House members calling for either the start to an official inquiry or an outright impeachment vote on Trump has grown to 52, according to a list maintained by NBC News.

That includes several committee chairs, several members of the Judiciary Committee — which would consider possible articles of impeachment first — lawmakers from safe districts and swing districts, and one Republican: Rep. Justin Amash of Michigan.

But it doesn't count a hard-to-quantify set of House Democrats who, without being held in check by Pelosi, would be ready now to hit the start button on impeachment. Democratic insiders say there's a significant chunk of the caucus showing deference to Pelosi either because they agree with her more methodical strategy, because they believe she's proved her acumen or because they don't want to publicly challenge her.

Some lawmakers acknowledge privately that she and her team are the only things standing in their way.

"Holding back for now waiting to see what leadership wants to do," one House Democrat said in a text message to NBC News earlier this week. "However if judiciary committee votes out articles of impeachment I will vote in favor of."

That lawmaker asked to remain anonymous because he has not publicly announced that he already has made up his mind that the president has committed impeachable offenses.

The figures also don't count a group of Democrats who say they will vote to start impeachment proceedings if Trump continues to defy subpoenas for witness testimony and documents from House committees. They are waiting to see whether the House votes to hold Trump administration officials in contempt — an action that could come as early as the second week of June — whether federal courts compel them to comply with the subpoenas, and whether they still refuse.

Rep. Stephanie Murphy, D-Fla., a leader of the House's centrist Democratic Blue Dog Coalition, and Rep. Harley Rouda, D-Calif., are among the members who have publicly said they fall into that category since Mueller made his statement this week.

Undoubtedly, Pelosi and Trump were spared a bit by the fact that Mueller spoke during a congressional recess, meaning that lawmakers lobbying for faster action on impeachment weren't able to buttonhole their colleagues in Capitol cloakrooms and hallways or make their case at caucus meetings.

"Otherwise they would have been calling in pizza. It would have been a late night hearing everybody out," said Dean Aguillen, a former senior adviser and member-services director for Pelosi. "Sure, next week they're going to be there, but it's not the immediate fervor."

While a member might move from the "no" camp to the "yes" camp on starting a formal probe, it is highly unlikely that anyone would reverse course after calling for an impeachment investigation.

It won't be clear until the House reconvenes next week whether the surge in pressure on Pelosi turns into a bona fide tide. She has argued, to great effect with her caucus, that there are significant risks in rushing toward impeachment when the public isn't supportive of the move and it would take 20 Republican votes in the Senate to oust the president.

Part of the Democratic strategy is rooted in concern that forcing an impeachment showdown, especially one that fails to result in Trump's removal from office, would benefit the president politically. Never mind the prospect — more unlikely than it is conceivable — that he could be impeached, removed from office and re-elected.

But Pelosi has also said the House should not choose to impeach or avoid impeachment based on political considerations.

Mueller found that he could not exonerate the president, and he has now given a near-equivalent of public testimony to that conclusion. So it stands to reason that the longer Democrats wait to start a formal process, the more it will look like they are not confident the Mueller report includes evidence of possible high crimes and misdemeanors.

Perhaps most Democrats will, or already have, reached that conclusion.

It’s not clear that there are enough votes now — or that there ever will be — to impeach Trump.

But if the vast majority of Pelosi's caucus believes that Mueller did produce enough to merit an official inquiry, it's hard to see how holding them back would be a decision based on anything other than politics.