For three years in a row, Justin Trudeau and his family have spent their Christmas vacation in the Caribbean.

In 2014, Trudeau took his family to Bell Island, the private retreat of the billionaire philanthropist and Trudeau family friend, the Aga Khan.

That 2014 trip, though, did not cost the federal treasury a dime as Trudeau, at that time, was an ordinary MP, the leader of what was then the third party in the House of Commons. His personal travel was, presumably, paid for with his own funds.

But Trudeau’s status, of course, changed in the fall of 2015. He had become the country’s prime minister and, as with any prime minister, he was assigned a protective detail by the RCMP. Notably, it is the RCMP and not the PMO which makes any decision about the size of that detail and what procedures and equipment that detail will use to keep the PM and his family safe.

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That detail went with him when he took his family on a Christmas vacation to St. Kitts in 2015 and that detail was also protecting him when he returned to the Aga Khan’s private island in the Bahamas in 2016.

The federal treasury has taken a big hit for those last two vacations with the bill topping more than $300,000 — and more than two-thirds of that is the incremental or additional overtime, per diem, and hotel bills for the RCMP security detail.

The RCMP released the final bill for the Bahamas trip on Aug. 25, in response to a request filed under federal access to information laws by Global News back on Jan. 5. The final RCMP bill was more than $150,000 for Trudeau’s seven days on the Aga Khan’s island, more than twice what the RCMP initially disclosed to Parliament last spring.

Judging by reaction on radio call-in shows and on social media, Canadians appear to have mixed feelings about these costs. Many shrug, saying the cost of protecting a prime minister is whatever it is going to be and prime ministers and their families deserve a holiday just like anyone else.

Others, notably the opposition Conservatives, say the prime minister ought to have a better regard for the public purse when he plans his holidays. Conservative MP Peter Kent this week called the bill for Trudeau’s holidays “unacceptable” and called on him to vacation somewhere in Canada for the remainder of his current mandate.

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On Wednesday, at the end of a two-day cabinet retreat here, Trudeau was asked where he was planning to vacation this Christmas. He declined to say.

WATCH: Prime Minister Justin Trudeau says inflated vacation costs due to RCMP, security detail

1:00 Trudeau says inflated vacation costs due to RCMP, security detail Trudeau says inflated vacation costs due to RCMP, security detail

Trudeau is not the first prime minister to be grilled by opponents and the press about the use of public resources for private purposes. Trudeau’s predecessor, Stephen Harper, for example, was pilloried by Liberals for the using an RCAF Challenger jet to go to Boston in 2011 to watch the Vancouver Canucks play the Bruins in the Stanley Cup final that year.

And prime ministers Jean Chretien, Brian Mulroney, and Pierre Elliott Trudeau also drew fire for their vacation habits.

But Justin Trudeau’s 2016 Bahamas trip is in a separate category from the rest and he faces a different political peril that has nothing to do with the cost of the trip.

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The Bahamas trip is the first prime ministerial vacation that has sparked an investigation by the House of Commons Conflict of Interest and Ethics Commissioner, Mary Dawson. The office of the ethics commissioner is a relatively new one, established in 2006 by the Harper government.

One of Dawson’s chief responsibilities is administering the Conflict of Interest Act. Dawson is investigating the Trudeau Bahamas trip for violations of two separate provisions of the Act.

READ MORE: 2nd request for ethics investigation sent to watchdog

If Trudeau is found to have been in contravention of either provision, he will be the first prime minister in history to have been found to have violated a federal law while he was in office.

The sanctions available to Dawson are minor. Trudeau would get the equivalent of an administrative slap on the wrist. But such a sanction would be presumably priceless to the opposition as they would be able to brand Trudeau a scofflaw, a sitting prime minister who believes he can choose which laws he will obey and which laws he will not.

Dawson has had this investigation open for nearly 10 months now and neither she nor Trudeau can explain why.

Trudeau, on Wednesday, told reporters that Dawson has asked any MP, including himself, who is under investigation not to discuss investigations until they are completed. Dawson’s office has repeatedly said it cannot say anything about any investigation until it is completed.

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The first charge levelled at Trudeau is that he placed himself in a conflict of interest in accepting the hospitality of the Aga Khan. That’s because the Aga Khan is the chairman of the Aga Khan Foundation and that foundation is registered to lobby the government of Canada for money to fund the foreign aid projects it works on.

The Aga Khan Foundation has received tens of millions of dollars over the last decade or so from the federal government, money it uses to improve the lives of people living in developing countries. The foundation was a favourite of the previous Harper government and it continues to receive support from the Trudeau government.

That said, the Aga Khan Foundation competes, if you will, against other charitable organizations like World Vision Canada, Oxfam and many others for scarce Canadian foreign aid dollars.

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To the extent that the prime minister receives gifts in the form of a free holiday from the head of a group competing for federal grants, the argument could be made that Trudeau violated the following provision of the Conflict of Interest Act:

“No public office holder or member of his or her family shall accept any gift or other advantage, including from a trust, that might reasonably be seen to have been given to influence the public office holder in the exercise of an official power, duty or function.” Tweet This

Trudeau has always maintained that the Aga Khan is a long-time friend of the Trudeau family and that the 2016 vacation should be viewed in that light, not in the light of a “public officer holder” receiving “a gift or other advantage” from someone seeking to influence the behaviour of said public office holder.

It will be up to Dawson to adjudicate what is arguably a grey area on that issue.

But the second accusation that Trudeau faces seems to be much more of a black-and-white issue.

The act states that “No minister of the Crown, minister of state or parliamentary secretary, no member of his or her family and no ministerial adviser or ministerial staff shall accept travel on non-commercial chartered or private aircraft for any purpose unless required in his or her capacity as a public office holder or in exceptional circumstances or with the prior approval of the Commissioner.”

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Trudeau, by his own admission, used the Aga Khan’s private helicopter to make the 40-minute trip from the airport in Nassau to Bell Island.

Trudeau has been asked repeatedly by reporters and by MPs about that helicopter use. He has never offered either exception — that there was an emergency or that he had prior approval from Dawson — as an excuse.

Opposition politicians are expected to raise this issue once again next week when the House of Commons returns from its summer recess.