Timeline: Key moments that led to Biden's historic withdrawal

• Trump, who would prefer to run against Biden, has been preparing a plan of attack should Vice President Kamala Harris be the new Democratic nominee, Axios' Mike Allen and Jim VandeHei reported.

The Trump-Biden debate

While there have been longstanding questions about the president's age, Biden's debate performance in late June — where his opponent Trump also told some 30 lies — shifted those concerns into overdrive.

• During the debate, Biden — who would be 82 at the start of a second term — was slow to answer in some instances, and struggled to form coherent arguments.
• Worries about his candidacy swiftly spread among lawmakers, staff and donors in the days that followed.
• Biden's own insistence that he was staying in the race and his campaign's efforts to quell concerns failed to stamp out the push to replace him.

Media appearances

In a bid to prove his poor debate performance was a one-off, the Biden campaign arranged a series of media appearances for the president.

• His first TV interview after the debate on July 5 — with ABC News' George Stephanopoulos — ultimately failed to assuage concerns.
• "If the Lord Almighty came down and said 'Joe, get out of the race,' I'd get out of the race. The Lord Almighty's not coming down," Biden said.

Zoom in: Biden has continued to make minor flubs in other appearances as well as some bigger ones, like accidentally calling Ukrainian President Volodymyr Zelensky "President Putin" at a NATO summit on July 11.

• His recent interviews have also raised questions about the kind of control the Biden team exerts over his appearances.
• The campaign requested a Wisconsin radio station cut portions of its interview with the president, and provided both that station and another one in Pennsylvania questions to use in advance.

Lawmakers start calling on Biden to step aside

Days after the debate, Rep. Lloyd Doggett (D-Texas) became the first Democrat in Congress to publicly call for Biden to bow out.

• More than 25 others have since followed suit.

• The pressure has been strongest in the House, though Democratic senators Sens. Peter Welch (D-Vt.), Jon Tester (D-Mont.), Martin Heinrich (D-N.M.) and Sherrod Brown (R-Ohio) — did publicly call on Biden to drop out.
• Donors, most prominently George Clooney, also piled on pressure.

Top Democrats ramp up pressure

Last weekend's attempted assassination of Trump temporarily quieted the turmoil over Biden's candidacy, but congressional Democrats revived the effort afterward, which took on a new tenor as Democratic heavy-hitters joined the fray.

• On July 17, Rep. Adam Schiff (D-Calif.), the Democratic candidate for U.S. Senate in California, became the most high-profile elected Democrat to publicly call for Biden's withdrawal from the race.
• Senate Majority Leader Chuck Schumer (D-N.Y.) and House Minority Leader Hakeem Jeffries (D-N.Y.) also privately confronted the president about the viability of his candidacy.
• Former House Speaker Nancy Pelosi conveyed to Biden and the campaign that his staying on the ticket could spell political peril for the party, Axios' Hans Nichols reported.
• Jeffrey Katzenberg, co-chair of the Biden campaign, privately warned Biden this week that donors' checks were drying up, Semafor reported.

The bottom line: By July 18, top Democrats told Axios' Mike Allen and Jim VandeHei that Biden could drop out as early as the weekend.

Go deeper: Biden's political isolation deepens as pressure to step aside builds