It's also -- in its own way -- largely meaningless.

The milestone is that 118 House Democrats -- half their caucus there -- have called for the start of an official impeachment inquiry into Trump, a significant number of legislators, who include the far left of the party but also some members who flipped GOP districts last fall and even a few allies of House Speaker Nancy Pelosi.

It's clear that the momentum of the party is toward impeachment even if party leaders like Pelosi, who recalls firsthand backlash to the impeachment of President Bill Clinton and insists on a methodical step-by-step process focused on obstruction of justice.

But even at more than 50% of the Democratic caucus, that's still less than a third of the full House, not to mention Democrats control only half the Legislative Branch. That math is not lost on Pelosi, who once told David Axelrod's "The Axe Files" podcast that among the chief political lessons she learned from her father -- Baltimore mayor and Democratic ward leader Thomas D'Alesandro -- was "I learned how to count."

This growing public support of Democratic lawmakers demonstrates how far they've come since last year, when it was just a few actively pursuing it in part because Democrats were waiting to see what was in special counsel Robert Mueller's report on Russian election interference.

While Mueller did not overtly call for impeachment or recommend charges against Trump or his aides, many Democrats increasingly argue that the 10 instances for which Mueller presented evidence of obstruction of justice by Trump are enough to pursue impeaching him -- though it's not clear when or if the rest of the party will ever agree.

Pressure on Pelosi

One of the reasons the number behind the impeachment inquiry movement is significant is in part the fact how Democratic leaders -- including Pelosi -- have cited the size of bloc as a reason not to proceed.

Back on June 11, CNN's Manu Raju asked Pelosi how she'd react if a majority of the caucus supported an impeachment inquiry.

JUST WATCHED Pelosi tells CNN: impeachment inquiry 'not off the table' Replay More Videos ... MUST WATCH Pelosi tells CNN: impeachment inquiry 'not off the table' 01:55

"It's not even close in our caucus," she told him back then.

"But eventually?" he followed up.

"Nothing is as divisive in our country, in my view, than impeachment," she ultimately said, after pointing out that Democrats were pursuing testimony from Trump officials by attempting to pursue enforcement of their subpoenas in court.

On Friday, Pelosi repeated her previous comments focusing on her party's investigations of the Trump administration and saying "Democrats in the Congress continue to legislate, investigate and litigate."

"In America, no one is above the law," Pelosi said in a statement that outlined Democrats' efforts. "The President will be held accountable."

Reaching this half-margin threshold will certainly amplify pressure on Pelosi to bless the effort and put her political weight behind it. She has claimed to not be opposed to impeachment, but she certainly hasn't been helping it along. And she's pointed out the political risk in impeaching Trump when there is essentially zero chance a Republican-controlled Senate would vote to remove him from office. From that perspective, impeachment would be a political exercise.

That doesn't matter to a lot of Democrats, particularly younger progressives, who say that pursuing impeachment and calling out Trump for alleged wrongdoing is a moral obligation.

JUST WATCHED Analyst on impeachment: Dems are speaking the magic words Replay More Videos ... MUST WATCH Analyst on impeachment: Dems are speaking the magic words 05:17

What's also not clear is if Trump administration officials who have refused to take part in congressional oversight will participate in hearings specifically geared toward impeaching their boss. (Spoiler alert: they probably won't).

A milestone that's also meaningless

For all the importance of 118 Democrats supporting impeachment, it is also meaningless.

For starters, 118 is a lot fewer than 218, which is the number of votes needed to actually impeach the President if Democrats do go forward with an impeachment inquiry and do find evidence he committed the "high crimes and misdemeanors" the Constitution requires for impeachment.

And support for an impeachment inquiry does not equal support for articles of impeachment. Rep. Al Green of Texas has routinely tried to get the House to vote on actual articles of impeachment. The House soundly rejected his attempt to impeach Trump for bigotry and racism rather than obstruction of justice in July, and 95 Democrats supported the proposal

If Democrats do pursue impeachment, they will be flying somewhat in the face of public opinion if they move toward impeaching Trump. A majority of Americans -- 54% -- opposed impeachment when CNN and SSRS asked the question in a June poll. But a strong majority of Democrats -- 76% -- supported it.

An inquiry that's already happening

Another complicating factor: Starting an impeachment inquiry actually doesn't require any specific number of Democrats or lawmakers.

Rep. Ted Deutch of Florida, who sits on the House Judiciary Committee, is one of the latest Democrats to publicly call for an impeachment inquiry -- number 116 by CNN's count -- but he also said that Democrats' many investigations of Trump essentially add up to the fact that an inquiry is already occurring.

In a piece for the Sun-Sentinel , Deutch noted that Trump claimed victory after Mueller's testimony before Congress, which Deutch admitted was not a "summer blockbuster," but which he said confirmed conclusions of Mueller's report, including evidence of obstruction of justice by the President.

"Sorry, Mr. President, the question is no longer whether the House should vote to proceed with a formal impeachment inquiry. The inquiry has already begun," he wrote, noting the committee can refer articles of impeachment to the full House at any time.

"No additional step is required," Deutch later added. "No magic words need to be uttered on the House floor. No vote to authorize an impeachment inquiry is necessary."

But Elie Honig, a former federal prosecutor and CNN legal analyst, said that courts might look differently at compelling administration officials to testify or turn over documents if House Democrats are officially pursuing impeachment.

"But the House is also undercutting itself by a failure to commit to what it's doing," Honig said, adding "The more formal and concrete the House's inquiry is, the better argument they have in court."

Impeachment and the 2020 election

And the impeachment conversation is not just happening on Capitol Hill.

For Democrats running for President, the subject rarely comes up on the campaign trail from voters, as New York Times reporter Jonathan Martin recently wrote . But those 2020 hopefuls expressed both sides of the impeachment question during CNN's Democratic presidential debate in Detroit.

Sen. Michael Bennet of Colorado said impeachment would ultimately be fruitless if the Senate acquitted Trump and he would be able to argue vindication.

"President Trump would be running saying that he had been acquitted by the United States Congress," Bennett cautioned.

Former HUD Secretary Julián Castro shot back that the opposite would be true.

"The Mueller report clearly details that he deserves it," Castro said, noting the 10 examples of possible obstruction of justice examined by the report. "And what's going to happen in the fall of next year, of 2020, if they don't impeach him, is he's going to say, 'You see. You see. The Democrats didn't go after me on impeachment. And you know why? Because I didn't do anything wrong."

This story has been updated with additional developments Friday.