A veteran of Washington politics for more than 50 years, Biden has weathered storms like few other candidates in modern history.

But he met his match in former House Speaker Nancy Pelosi, who remains perhaps the party's most important political strategist despite having ceded her leadership role early last year.

Pelosi led Democratic House majorities from 2007 to 2011 and from 2019 to 2023, anchored by victories in critical swing districts across the country. In addition to Pelosi's legendary whip operation on the House floors, she has a keen ability to sense when candidates are in trouble in their districts.

And based on data from multiple pollsters, Biden continued to trail Trump after the debate. The dynamic that Biden hoped to reverse simply hadn't changed.

Pelosi privately told Biden and several colleagues that she found it incredibly difficult to see a path forward for his candidacy, The New York Times reported. She also reportedly worked behind the scenes to get him to drop out. Her influence has been so significant that Biden himself considered her the "main instigator" of the situation, as the Times wrote.

She also apppeared on MSNBC's "Morning Joe" (one of Biden's favorite programs) and said that it was up to him to decide if he wanted to stay in the race, even though he'd already clearly and repeatedly said he was staying in it. Notably, she did not explicitly endorse Biden in the interview and said "time is running short" for him to make a decision, which, again, he'd already made.

Her statements and backroom maneuvers undoubtedly gave her Democratic congressional colleagues the cover they needed to call for Biden to step aside.

Pelosi is a Democratic Party institutionalist through and through.

She has worked with Biden for decades and helped shepherd key pieces of legislation, including the bipartisan infrastructure law and the Inflation Reduction Act, through the House. When Biden served as vice president under President Barack Obama, she did the same in getting the Lilly Ledbetter Fair Pay Act and the Affordable Care Act through Congress and to the president's desk.

Pelosi has long touted her strong working relationship with Biden.

But the state of the 2024 presidential campaign was a critical crossroads for Pelosi.

She knew that Biden continued to falter in polling after the June debate. And swing-district Democrats, wary of Biden potentially tamping down enthusiasm at the top of the ticket, clearly relayed their concerns to her about his standing.

Pelosi, long known for her blunt manner, didn't lead the House Democratic Caucus for 20 years by accident.

In withdrawing from the race and backing Harris to succeed him, Biden demonstrated the sort of passing of the torch that many Democrats had hoped to see earlier in his term.

But it highlighted the enduring power of Pelosi, whose influence continues to profoundly shape the Democratic Party.