There's a mad dash to track anyone who has come in direct contact with Trump over the last week or so to get tested for the coronavirus. The problem? It's a really long list because Trump has been full steam ahead campaigning and holding events in the middle of a pandemic.
That makes contact tracing nearly impossible.
"It's hard to actually get our heads around the number of people that could have been exposed to the president, and I think the White House is trying really hard to identify everyone in his orbit," said MaryAlice Parks, deputy political director at ABC News. "But we're talking about dozens of people who are in regular contact with the commander in chief. Secret Service, local police, his staff, residence staff."
"Testing is a very important part of an infection control strategy, but testing alone is not an infection control strategy," said Dr. Michael Ben-Aderet, associate director epidemiology at Cedars-Sinai. "Even if a test is negative on day five, it doesn't mean that you're not at risk on day nine or 10."
Below is a review of the president's activities leading up to his COVID-19 diagnosis.
Saturday - Sept. 26
Last Saturday, Trump announced the nomination of judge Amy Coney Barrett to the Supreme Court, with a few hundred people in attendance, most not wearing masks. Sen. Mike Lee of Utah was seen at the event hugging attendees, he's now tested positive along with Notre Dame president John Jenkins. First lady Melania Trump was also at that event. The thousands in attendance at Trump's campaign rally that night in Pennsylvania have been urged to get tested if feeling sick.
-- Trump announces the nomination of Barrett to the Supreme Court. Lee and Jenkins, who were at the Rose Garden event, announced on Friday they have tested positive for the virus.
-- Trump holds a campaign rally in Harrisburg, Pa., attended by thousands of supporters, many not wearing masks.
Sunday - Sept. 27
Trump held events Sunday and Monday at the White House before the Cleveland debate Tuesday night where senior aide Hope Hicks was by his side.
-- Trump visits his golf course in Sterling, Va. and holds a late afternoon news conference in the White House briefing room.
-- Trump and his wife hold an early evening reception for Gold Star Families on the White House State floor.
Monday - Sept. 28
-- Trump surveys a truck produced by Lordstown Motors on the White House South Lawn at an event attended by two members of Congress and three representatives from the Lordstown, Ohio, manufacturer.
-- Trump holds a Rose Garden event to announce an administration effort to distribute millions of coronavirus test kits to states. The event is attended by administration officials including Vice President Mike Pence, members of Congress and state officials.
Tuesday - Sept. 29
Trump travels to Cleveland for the first presidential debate against Joe Biden.
"I don't wear masks like him," Trump said at the debate, mocking Biden's use of a mask. "Every time you see him, he's got a mask. He could be speaking 200 feet away from it, and he shows up with the biggest mask I've seen."
White House aide Hope Hicks is part of a large entourage that travels to Ohio with Trump aboard Air Force One for the debate, including members of the Trump family. Trump's family was seen at the debate not wearing masks, breaking the audience rules, but so far, they've tested negative.
Wednesday - Sept. 30
Trump attends a fundraiser in Minnesota at a private home. He also attends an outdoor rally in Duluth. Hicks is among the White House aides who accompany Trump on the trip. She feels unwell on the return trip and isolates herself aboard Air Force One.
Thursday - Oct. 1
Hicks tested positive for COVID-19 Thursday.
Trump flies to his Bedminster resort in New Jersey for a private fundraiser. Several aides who were in proximity to Hicks scrap plans to accompany Trump. White House officials say they learned of Hicks' positive test soon after Trump boarded Marine One to start his journey to New Jersey.
Trump announces in an evening interview on Fox News that he and the first lady are being tested for the coronavirus. He later tweets that they will "begin our quarantine process!"
Friday - Oct. 2
Trump tweeted Friday before 1 a.m. that he and the first lady tested positive for coronavirus, writing that they "will begin our quarantine and recovery process immediately."
Dr. Sean Conley, physician to the president, releases a statement that the president and first lady "are both well at this time, and they plan to remain at home within the White House during their convalescence."
White House officials say Trump and his wife are experiencing mild symptoms, and that senior advisers who were in close contact with the president and Hicks have tested negative.
White House staff later says Trump is experiencing "fatigue." Trump flies by Marine One to Walter Reed Medical Center, a military hospital, on the advice of his physicians. White House officials say Trump will remain there for a "few days."
Vice President Mike Pence tested negative for the virus Friday morning and "remains in good health," his spokesman said. Both Democratic presidential nominee Joe Biden and his running mate Kamala Harris have tested negative, their campaign said.
The Associated Press contributed to this report.