Editor’s Note: Julian Zelizer, a CNN political analyst, is a professor of history and public affairs at Princeton University and author of the forthcoming book, “Burning Down the House: Newt Gingrich, the Fall of a Speaker, and the Rise of the New Republican Party.” Follow him on Twitter: @julianzelizer. The views expressed in this commentary are his own. View more opinion at CNN.

CNN  — 

House Speaker Nancy Pelosi is in the middle of a high-stakes showdown with the President. Since announcing her support for an impeachment inquiry, the investigation has rapidly accelerated. News reports, along with the whistleblower complaint, rough White House transcript and President Trump’s own comments revealed his efforts to lean on foreign leaders to investigate his leading 2020 rival, Joe Biden. Each day brings new evidence that the President welcomes election interference from foreign countries and that the behind-the-scenes diplomatic interactions to that end were worse than they first appeared.

Julian Zelizer

There has been growing support for impeachment among independents and Republicans. Meanwhile, Congressional Democrats are increasingly confident talking about the need to vote for articles of impeachment and remove the President from office.

Yet President Trump is not giving in easily. He is intensifying his attacks on Democrats, the news media and Biden. Trump has repeatedly claimed the former vice president called for the firing of a Ukrainian prosecutor who was “investigating his son.” But there is no evidence Hunter Biden was ever under investigation, and there is no evidence of wrongdoing from either Joe or Hunter Biden. Regardless, Trump insists that he did nothing wrong in asking Ukraine President Volodymyr Zelensky to investigate the Bidens and doubled down by publicly calling on China to do so as well.

While Republican Sens. Mitt Romney and Ben Sasse have spoken out against the President’s comments, most congressional Republicans are standing firm. And the conservative news media, acting as the President’s firewall, has been broadcasting stories that echo Trump’s message.

In this pivotal moment for the President and our democracy, what is Pelosi’s endgame?

Historically, you can learn a lot from a speaker from the sayings he or she likes to use. Speaker Sam Rayburn, the Texan who held the position for much of the time between 1940 and 1961, had a number of famous sayings, like, “if you want to get along, go along,” that captured his approach to legislating.

The same is true with Speaker Pelosi, whose repeated aphorisms offer a window to what comes next.

‘If you don’t have 218 votes, you’re just having a conversation’

Speaker Pelosi is a meticulous vote counter. While she is often sympathetic to colleagues who have big ideas and visionary agendas, what drives her final decision more than anything else is whether a specific proposal has the 218 votes necessary to make it through the House. If it doesn’t, she is extremely leery about bringing something to the floor.

After months of resistance, Pelosi announced the launch of an impeachment inquiry after news of the whistleblower complaint sparked a groundswell of support among House Democrats. Currently, Pelosi is allowing the investigation – and the ensuing drama – to play out until she has secured total control of her caucus. She knows that Republican support remains doubtful, and she wants to be 100% certain that if and when she brings articles of impeachment to the floor, she has the votes needed to get them through. Once she has at least 218 votes, she won’t hold off for much longer.

‘Nobody gives you power, you have to take it from them’

Speaker Pelosi understands that President Trump is going to throw everything he has at her party in an effort to save himself. He is likely to spread false rumors, endorse conspiracy theories and attack the character of everyone who he believes to be a threat.

Since the ball remains in her court, Pelosi will continue to drive the investigation forward for as long as possible with the hope of uncovering unassailable evidence of abusing the power of the executive office that will drum up support among independents and Republicans, with the slim chance that the Republican dam in the Senate will finally break.

While there has been some speculation about whether President Trump will resign, Pelosi doesn’t come from that school of thought. She is not counting on the conscience of her opponents, and will try to force their hand instead. She knows that Trump and his party will not relinquish power unless electoral pressure in conservative states forces senators in the GOP to join Democrats in a vote to remove the President. If Senate Republicans won’t do so, she wants to present a case that is so strong that the House vote on impeachment will leave a devastating mark on the President going into 2020.

‘Public sentiment is everything’

Abraham Lincoln once said, “In this age, and this country, public sentiment is everything. With it, nothing can fail; against it, nothing can succeed.”

Pelosi, who has previously resisted impeachment because she believes Democrats need public opinion on their side, likes to share this quote with her colleagues. Right now, the strategy appears to be working as support for impeachment is higher than it was at this point in the impeachment proceedings against Presidents Richard Nixon or Bill Clinton.

It’s no coincidence that the impeachment inquiry was launched after the whistleblower filed a complaint claiming President Trump asked a foreign leader to investigate his political rival at home, sources told CNN and the Wall Street Journal. Unlike the findings from the Mueller report, the Ukraine whistleblower complaint presents a scenario that Americans can easily understand. Despite criticism for not moving earlier on impeachment, Pelosi held firm until public opinion moved more legislators within her own caucus to call for action.

Now she continues to wait while the President digs himself deeper in a hole. Democrats are gaining public support and that is what makes things perilous for the administration. Pelosi will continue to wait until the numbers rise high enough to create a firewall for Democrats against the inevitable backlash.

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    These three quotations offer a powerful window into the mind of a Speaker who is intent on holding the President accountable. While it took her longer to get the impeachment ball rolling than many Democrats like, Pelosi is ready to put up a fight.

    Even Trump, who has failed to give Pelosi one of his famous nicknames, has said, “I don’t think she’s scared of anything. I think she’s a smart woman and I think she knows exactly what she’s doing.” It is likely that Trump understands that she might very well be the most formidable opponent that he has faced.