Image copyright Reuters Image caption Andrew Scheer celebrates after winning the leadership

From UK Prime Minister Boris Johnson to US Senator Ted Cruz, politicians have landed in hot water for having dual citizenship. Now, a Canadian politician finds himself simmering in the same pot.

It should go without saying that Andrew Scheer - the leader of Canada's Conservative Party and Prime Minister Justin Trudeau's biggest challenger in the upcoming election - is as Canadian as maple syrup pie.

Born in Canada's capital, he cheers for the Toronto Blue Jays and has made his home in the prairie city of Regina, Saskatchewan.

But there is a blemish on his Canuck bona fides - he also holds citizenship with the US.

The revelation has left Mr Scheer vulnerable to accusations of hypocrisy, given that he and members of his party have previously questioned the loyalties of political opponents who held dual citizenship.

Now, there is nothing unusual about Canadians holding dual citizenship with the US - there are approximately 340,000 Americans immigrants who attained Canadian citizenship and there are many natively born Canadians who achieved American citizenship through one of their parents.

The latter route is how Mr Scheer became an American. His father was born in the US, moved to Canada and married his Canadian mother. Mr Scheer was born in Canada's capital city of Ottawa, and his father applied for US citizenship for him at birth.

"It's not a big deal to have dual citizenship here in Canada," he told media on Friday.

But things that are not a big deal for the public can become a big deal for politicians, examples from around the world show.

Dual-citizens of the world

Ted Cruz, the Texas senator, was mercilessly ridiculed by Donald Trump during the 2016 presidential primaries because he was born in Canada.

In the US, the president must hold American citizenship at birth, and Cruz's Canadian citizenship (that he renounced in 2014) was a "question mark" hanging over his candidacy, according to Mr Trump.

That rule was at one time a perk for Boris Johnson, who in 2012 told US chat show host David Letterman that he could "technically speaking" become US president.

Born in New York, the PM said he was thinking about relinquishing his US citizenship as far back as 2006, although it wasn't official until 2016.

"The reason I'm thinking I probably will want to make a change is that my commitment is, and always has been, to Britain," he said in 2006 on his personal blog.

And in Australia, section 44 of the nation's constitution forbids anyone holding citizenship of another country from running for parliament. The law was basically forgotten until a succession of disclosures led to five Australian MPs were ousted from parliament.

Image copyright Reuters, Getty, EP Image caption Five Australian MPs (including deputy PM Barnaby Joyce, top left) were disqualified from parliament because of holding dual citizenship

Canada has no such law, but that hasn't stopped politicians from using an opponent's dual citizenship against them in the past, including Mr Scheer, who attacked governor general appointee Michaelle Jean in 2005 for having dual citizenship.

"I have a few quick questions for anyone who thinks that Michaelle Jean is a good choice to be our next GG," he wrote in a blog post.

"Does it bother you that she is a dual citizen (France and Canada)? Would it bother you if instead of French citizenship, she held US citizenship?"

That criticism has left Mr Scheer himself open to attack, says political scientists Paul Hamilton, who teaches at Brock University.

"It seems odd that 15 years ago he was critical of this but never once revealed that he was a dual citizen," he says.

Why do we care?

Mr Hamilton says most Canadians do not care about whether someone holds dual citizenship, but that questions about conflicts of interest for public officials can arise.

In the case of Mr Scheer, who has held socially conservative views in the past, there is also the question of whether his politics might be a little too American, Mr Hamilton says.

"In this Trump time, I think it just makes it a little more questionable for some Canadians who are frankly, a little anti-American," he said.

"It's raising concerns."

But Mr Hamilton thinks these kinds of concerns are likely to just be a blip in the election cycle, especially considering Mr Scheer's weak cultural ties to the US.

Mr Scheer says has never voted in an American election, nor has he earned any income in the US.

Scheer decided to renounce his US citizenship after he was elected leader of the Conservatives, and submitted his paperwork in August, spokesperson Simon Jefferies told the BBC.

The process can take upwards of 10 months.