TORONTO — Canadian voters head to the polls Monday to decide whether to give Prime Minister Justin Trudeau a second mandate. Canada has a long history of reelecting its first-term prime ministers who have led parliamentary majorities, but after recent missteps and scandals, the telegenic Liberal leader has fallen back into a tight race with Conservative Andrew Scheer.

The vote will conclude an unusually cynical race that has been dominated by questions and attacks on the personal character and backgrounds of the party leaders as substantive discussions on policy have taken a back seat. Some have called it the Seinfeld Election (it’s been about nothing); others have lamented the American-style attacks. A Globe and Mail columnist dubbed it “The Most Depressing Election Campaign Ever.”

Who’s going to win?

Of the six party leaders, there are two clear front-runners: Trudeau, 47, and Scheer, 40.

There was much enthusiasm for Trudeau, the bilingual son of longtime Prime Minister Pierre Elliott Trudeau, when he first won election in 2015. He championed diversity, welcomed refugees, imposed a nationwide price on carbon and legalized recreational cannabis. The unemployment rate is at the lowest in decades.

But his image has been tarnished in the run-up to the election by scandals, including the revelation that he wore blackface and brownface as a younger man. Trudeau has apologized, but his rivals have seized on the opportunity to paint him as a “phony” who is “not as advertised.”

Scheer, an affable father of five, has struggled to define himself or attract voters outside of his base since winning the party leadership in 2017. He has come under attack for his opposition to abortion and for refusing to say whether he supports same-sex marriage. He has promised not to reopen the debate on either issue and to balance the budget within five years.

Scheer has also been on the defensive over his personal background. The Globe and Mail reported during the campaign that he misrepresented his experience in the insurance industry on his résumé and revealed that he is a dual citizen of Canada and the United States. Scheer said he sought in August to renounce his U.S. citizenship, but critics charged hypocrisy because he once questioned the dual citizenship of Michaëlle Jean, a former Haitian refu­gee who served as governor general, Queen Elizabeth II’s representative in Canada.

Who else is running?

New Democratic Party leader Jagmeet Singh, 40, has seen a bump in support since the campaign began. A practicing Sikh born to immigrant parents from India, he has earned praise for his response to Trudeau’s blackface scandal and for his debate performances. His candidacy has exposed a darker side of Canadian society: At a campaign stop in Montreal, a man suggested he remove his turban so he could “look like a Canadian.” Singh’s left-leaning party could siphon votes away from the Liberals.

Elizabeth May, 65, the U.S.-born leader of the Green Party, saw her poll numbers climb to historic highs before the campaign kicked off last month, but the party has since lost momentum. She has promised to create a “war cabinet” to combat climate change and to phase out fossil fuels by 2030. Her campaign has experienced some embarrassing gaffes, including using Photoshop to show her holding a reusable cup with a metal straw.

The separatist Bloc Québécois poses a serious threat to the fortunes of the Liberals and Conservatives in Quebec. The resurgent party is led by Yves-Francois Blançhet, 54, a former rock group manager nicknamed “The Goon.” He supports a controversial Quebec law that bans public employees from wearing religious symbols at work.

Then there’s Maxime Bernier, 56, the libertarian who founded the hard-right People’s Party of Canada last year after losing the Conservative Party leadership race to Scheer. Bernier has railed against multiculturalism, proposed building a “border fence” at the U.S.-Canada border and mocked Swedish climate change activist Greta Thunberg. His new party, however, is struggling, and Bernier, elected to Parliament in 2015 as a Conservative, could lose his seat.

What are the issues?

No single issue has dominated the campaign. The candidates have largely tried to address concerns over affordability in their platforms, with pledges to slash cellphone bills and offer boutique tax credits for middle-class families with children.

One of the main areas of disagreement is on the environment. Trudeau has promised to commit Canada to net-zero emissions by 2050 but has offered few details on how he’d get there. Scheer, by contrast, says his first order of business as prime minister would be to repeal the Liberal government’s carbon tax. The New Democrats and the Greens have criticized both parties for putting forth inadequate plans on climate change and have attacked Trudeau for buying the Trans Mountain pipeline last year. On climate change, Singh has said, Trudeau and Scheer offer a choice between “Mr. Delay and Mr. Deny.”

If the campaign is remembered for anything, it might be its uncharacteristically nasty tone. Candidates from all sides have participated in the mudslinging. A debate earlier this month quickly devolved into a six-way screaming match. Underscoring the souring of the political climate, Trudeau took the unprecedented step of wearing a bulletproof vest at a rally in Mississauga, Ontario, this month because of a security threat.

How do Canadians elect their prime minister?

Voters in each of 338 electoral districts, called ridings, elect a member to represent them in the House of Commons, the lower chamber of Canadian Parliament.

The suburbs outside Toronto and Vancouver and the province of Quebec are key battlegrounds where elections are won and lost.

Canadians do not vote directly for prime minister. The prime minister is the leader of the party that commands the confidence of the House of Commons — analogous to the speaker of the House of Representatives in the United States. If a party wins a majority of the seats — 170 or more — it forms the government and its leader becomes prime minister.

But polls show neither the Liberals nor the Conservatives are likely to win a majority.

What then?

There would be a minority government — and it could get complicated.

No matter the result on Monday, Trudeau will remain prime minister until he resigns or is dismissed. If neither happens, he gets the first crack at forming a new government.

This is where smaller parties can play kingmaker. Trudeau could try to put together a formal coalition, in which lawmakers from more than one party share cabinet seats, but the last time Canada saw such an arrangement was 1917. More common are informal coalitions, in which the governing party works with other parties to pass bills on a case-by-case basis.

The first test to see if the government has the confidence of the House is the “Speech from the Throne.” It’s written by the government to outline its agenda and is then put to a vote. If the government loses the vote, it collapses. The governor general can then ask the other parties to try to form a government or dissolve Parliament, forcing a new election.

The Conservatives would have few natural allies in a minority government. Singh already has ruled out propping up a Conservative minority government. He said last week he’d “absolutely” form a coalition with the other parties to block the Conservatives from holding power, but has since retreated from those remarks.

Philippe Lagassé, an international relations professor at Carleton University in Ottawa, says much will depend on the difference in seat count between the top two parties. If the Conservatives win by a wide margin, he said, Trudeau will come under “fairly significant” pressure to resign.