The first photo of Justin Trudeau in blackface makeup was released on Sept. 18. Within hours, more photos surfaced of Trudeau dressed up with a darkened face.

When pressed the next day to state whether there were any more such images, Trudeau, now the Liberal leader, said, "I am wary of being definitive about this."

How many photos do we know of?

There are least three photos and one video of Trudeau wearing racist makeup.

The story broke with the publication by Time magazine of a photo from a 2001 yearbook from the Vancouver private school West Point Grey Academy, where Trudeau taught. The school staged an Arabian Nights-themed gala. Trudeau dressed as Aladdin, in blackface and a turban.

Time reported that it obtained the photo from Vancouver businessman Michael Adamson, who was identified as being "part of the West Point Grey Academy community."

Trudeau is shown in this 2001 photo published in the yearbook of West Point Grey Academy, a private school where he was teaching at the time. (Time.com)

A second photo from the same gala surfaced later Sept. 18. It had been printed in the school's newsletter.

This image was part of an April 2001 newsletter from the West Point Grey Academy. (West Point Grey Academy)

Trudeau was asked by CBC News reporter David Cochrane if there were any other, similar incidents he should divulge. Trudeau said there was one other incident, dating from when he was in a high school talent show at Montreal's Collège Jean-de-Brébeuf. He wore blackface to sing Harry Belefonte's hit Day O (Banana Boat Song).

Trudeau pictured at Le Collège Jean-de-Brébeuf in the school talent show singing Day O and wearing makeup. (CBC)

The next day, Global News released a video it obtained of Trudeau, again in blackface. It came from an unidentified event, but the Liberal Party confirmed that it was indeed Trudeau in the 1990s. Global reported it obtained the video from a source in the Conservative Party.

The Liberal Party has confirmed a third instance of Trudeau in blackface. It appears to show Trudeau with his face and arms covered in black makeup, raising his hands in the air while laughing and sticking out his tongue. (Global News/The Canadian Press)

How did Trudeau react?

Trudeau held an emergency news conference on his campaign plane. He apologized and said he "should have known better."

"I take responsibility for my decision to do that. I shouldn't have done it," he said. "I should have known better. It was something that I didn't think was racist at the time, but now I recognize it was something racist to do and I am deeply sorry."

Watch Trudeau's full apology and answers to reporter questions:

Liberal Leader Justin Trudeau apologizes while answering reporters' questions in Winnipeg about the emergence of images of him in blackface in Thursday. 21:50

Why didn't this come up when Trudeau first ran?

Trudeau first ran for the Liberals in the riding of Papineau in 2008. He says he did not tell party vetters about the brown- and blackface incidents because he was embarrassed.

"I never talked about this. Quite frankly, I was embarrassed," Trudeau told reporters on Sept. 19. "It was not something that represents the person I've become, the leader I try to be, and it was really embarrassing."

The party's rules for vetting candidates state that a nominee has an ongoing obligation to "disclose to the national campaign chair any information that could impact upon their acceptability as a qualified nomination contestant or as a candidate of the party."

Trudeau said he didn't even tell his staff about his past until Time advised him that it was going to publish the story.

What if Trudeau resigned mid-campaign?

It would be unprecedented in Canadian politics, so political scientists have been mulling over how it might play out.

They all point to the Liberal Party's constitution — which outlines what happens when a leader resigns and an interim needs to be chosen — rather than the Elections Act. A leader dropping out mid-campaign is not explicitly mentioned in the party's constitution. One section does give some guidance, though: it states the national board of directors would appoint an interim leader in consultation with caucus.

But dealing with a caucus becomes tricky after Parliament is dissolved. Kelly Blidook, who teaches political science at Newfoundland's Memorial University, said he thinks the board "technically" could name an interim leader without caucus consultation.

"But I am reasonably certain in such a case that there would be a selective consultation of senior or longtime elected Liberals," he wrote in an email.

The timeline would be incredibly tight, though — maybe impossible.

"There is simply not enough time to formally select a new leader during the campaign," said Matthew Kerby, who has taught political science at Memorial and the University of Ottawa and now teaches at Australian National University.

"Strategically, it would be a terrible idea as it would leave the party rudderless and would also be a tacit admission of defeat before election day."

What has Trudeau said about resigning?

Asked on Sept. 18 if he should resign as Liberal leader, Trudeau argued that incidents like these should be approached on a "case-by-case" basis.

"There are people who make mistakes in this life and you make decisions based on what they actually do, what they did and on a case-by-case basis. I deeply regret that I did that. I should have known better, but I didn't," he said.

Asked the next day if he'd considered stepping aside to let someone else lead the party through the election, Trudeau did not answer directly but said he would "continue to do the work that is necessary to keep us moving forward in the right way."

How did the other leaders react?

Conservative Leader Andrew Scheer: A few hours after the first photo surfaced, Scheer said he was extremely shocked and disappointed.

"Wearing brownface is an act of open mockery and racism. It was just as racist in 2001 as it is in 2019," he said. "And what Canadians saw this evening was someone with a complete lack of judgment and integrity and someone who is not fit to govern this country."

NDP Leader Jagmeet Singh: Singh said Trudeau's behaviour was "troubling" and "insulting."

"It's making a mockery of someone for what they live and what their lived experiences are," he said. "I think he needs to answer for it. I think he needs to answer the question why he did that and what does that say about what he thinks about people who, because of who they are, because of the colour of their skin, face challenges and barriers and obstacles in their life."

Singh said it's not up to him to say whether Trudeau should be prime minister, leaving that decision to voters.

Trudeau and Singh spoke a few days later by phone. Singh said he would only take the call if the contents of their conversation remained private. He later confirmed they spoke.

"Mr. Trudeau did call me. We did have a chat. I said that I wanted to keep the conversation private because I didn't want to be used as a tool in his exoneration," Singh said. "But I also want to make it clear, it doesn't matter if he tells me anything. I'm not a proxy for the people of Canada."

Green Party Leader Elizabeth May: May tweeted Sept. 18 that she was deeply shocked.

I am deeply shocked by the racism shown in the photograph of Justin Trudeau. He must apologize for the harm done and commit to learning and appreciating the requirement to model social justice leadership at all levels of government. In this matter he has failed. —@ElizabethMay

The next day, she said she does not believe Trudeau is racist. "At that point in his life, I think you'd have to say he was unconsciously racist. I would not say today the man I know is a racist. But I could not imagine that photo, either."

Bloc Québécois Leader Yves-François Blanchet: Blanchet said he is "sincerely convinced" that Trudeau is not a racist.

"But I am as much sincerely convinced that it shows, or his reaction shows, or his lack of anticipation of this problem shows that he does not have the required qualities to be the prime minister of a country being a member of the G7."

People's Party Leader Maxime Bernier: Bernier tweeted that he wasn't going to accuse Trudeau of being a racist but he did think he was "the biggest hypocrite in the country."

"He's the master of identity politics and the [Liberals] just spent months accusing everyone of being white supremacists."

How did the Liberal Party react?

The Liberal Party confirmed that all the photos and the video were of Trudeau, but did not issue an official statement.

How have Liberal candidates reacted?

Greg Fergus, a black Liberal MP seeking re-election in Hull-Aylmer, Que., said Trudeau should be judged on his "great record" on promoting equality and diversity, not on things that happened nearly 20 years ago.

"I think those are really the measure of the man and that's the reason why I have confidence in his continuing leadership," he said.

Watch Fergus and other Liberal MPs of colour react:

Liberal MPs Greg Fergus, Iqra Khalid, and Sajjan Harjit, who served as defence minister, talk about why they are standing behind Liberal Leader Justin Trudeau, in light of the black- and brownface photos that have surfaced. 1:07

Omar Alghabra, who is seeking re-election as a Liberal MP for Mississauga Centre, said his heart sank when he saw the photos.

"The person I know of Justin Trudeau for the last seven or eight years is a champion against intolerance and racism. Not just lip service, but with real deeds and real action. That is the Justin Trudeau I know. I can't explain those pictures."

Amarjeet Sohi, who served as natural resources minister and is seeking re-election in Edmonton Mill Woods, issued a strong statement condemning the images.

"I was very disheartened and disappointed to see these images. These indefensible images bring back many painful memories of racism that I and other racialized Canadians have experienced throughout their lives," he said.

Please see my statement on the images of the Prime Minister that have surfaced over the last 24 hours:<a href="https://twitter.com/hashtag/yeg?src=hash&ref_src=twsrc%5Etfw">#yeg</a> <a href="https://twitter.com/hashtag/cdnpoli?src=hash&ref_src=twsrc%5Etfw">#cdnpoli</a> <a href="https://t.co/kwTtI0pqZW">pic.twitter.com/kwTtI0pqZW</a> —@SohiAmarjeet

Catherine McKenna, who served as environment and climate change minister under Trudeau, said what the Liberal leader did was a mistake but she would not be running if she didn't believe in him.

Watch McKenna explain why she is standing behind him:

Ontario MP Catherine McKenna, who served as environment and climate change minister, reacts to the photos of Justin Trudeau in black- and brownface. 0:36

Trudeau said that when he darkened his face 20 years ago, he did not realize it was a racist act. He said he recognizes now that it is.

But many Canadians have said that they don't consider it racist and that it was just part of a costume.

This article explains why wearing brownface or blackface is considered "reprehensible."