Prime Minister Justin Trudeau threw some light jabs during a photo-op with kids in a Brooklyn boxing ring last week. But bigger punches about Trudeau's trips to the United States are being thrown at home, mainly from the Conservative opposition.

Over the past two months, Trudeau has spent at least 13 days in the U.S. — including travel days. These are the days that have been confirmed by the Prime Minister's Office and Trudeau's travel itineraries.

While there, Trudeau has split time between Washington and New York City, visiting both twice.

Opposition MPs pounced on the Liberals inside the House of Commons throughout March and April — criticizing Trudeau for "lavish meals" and photo-ops during his travels south.

PM Trudeau in the U.S.

March 9-11 (Washington) — State dinner, Oval Office meeting, State Department working lunch.

— State dinner, Oval Office meeting, State Department working lunch. March 16, 17 (New York City) — UN visit and meetings, gender equality award at Catalyst gala.

— UN visit and meetings, gender equality award at Catalyst gala. March 30-April 1 (Washington) — Attended Nuclear Security Summit, met with prime ministers from United Kingdom and India.

— Attended Nuclear Security Summit, met with prime ministers from United Kingdom and India. April 20-24 (New York City) — Signed Paris climate treaty agreement at the UN, boxing training photo-op, New York University Q&A, saw Hamilton on Broadway.

But the boxing — above everything else Trudeau has done in the U.S. — seemed to provide the most fodder for critics.

Interim Conservative Leader Rona Ambrose twice referenced it in the House of Commons last Thursday, while discussing the children's fitness tax credit, which the Liberals will be phasing out by the end of 2017. Trudeau's boxing was also brought up in separate remarks by Conservative MPs Denis Lebel and Alexander Nuttall.

"Now the prime minister can use those same tax dollars of families and fly to New York to work out in front of TV cameras, while families are struggling to pay for their kids' sports. Instead of focusing on self-promotion, will the Prime Minister focus on promoting children's fitness and reinstate the child fitness tax credit?," Ambrose asked.

A spokesman for the prime minister said costs for this kind of international travel, including accommodations and meals, are covered by Global Affairs Canada under the international conference allotment and are published annually in September. A breakdown of Trudeau's costs for the recent U.S. trips was not immediately available.

Expenses for the prime minister not covered by travel with an official delegation are disclosed quarterly on the prime minister's own proactive disclosure website, but no foreign expenses are listed for the most recent quarter, which ended March 31.

'3 days to sign a piece of paper'

A fundraising email sent out by the Conservative Party on Sunday afternoon blasted Trudeau for "self-promoting in the U.S.," criticizing the boxing stop in Brooklyn and for taking "three days to sign a piece of paper." Trudeau was in town to sign the Paris climate treaty agreement at the UN.

Andrée-Lyne Hallé, a spokeswoman for the PMO, brushed off the criticism in an email to CBC News.

QUICK WHAT RHYMES WITH CANADA <br>(Honor to meet you both) <a href="https://t.co/sP5sbYrkbq">pic.twitter.com/sP5sbYrkbq</a> —@Lin_Manuel

"We are proud of the work that we have been doing in the last six months and the prime minister is proud to represent Canada on the international stage," she said.

"Signing the Paris Agreement at the UN last Friday was an important step in the fight against climate change that over 150 countries are undertaking." Hallé said the boxing photo-op was part of a program to help disadvantaged kids.

Trudeau spent an additional day and a half in New York for "private appointments" — like his trip to see the immensely-popular hip-hop musical Hamilton on Broadway — before travelling to the cabinet retreat in Kananaskis, Alta.

The prime minister has also travelled extensively throughout Canada since taking power, including visits to towns and cities in New Brunswick, Nova Scotia, British Columbia, Quebec, Saskatchewan, Alberta, Ontario and a family vacation to Newfoundland.

What do the U.S. trips mean?

Debora VanNijnatten, who chairs Wilfrid Laurier University's political science department, said that while Trudeau has been abroad "a lot," she thinks the trips are warranted.

"He's got a lot of bridges to build, or rebuild, I would say, 'cause things have not been very overtly friendly over the last little while between the Harper government and the U.S. administration," VanNijnatten said, referring to former prime minister Stephen Harper and U.S. President Barack Obama's complicated relationship.

"Why wouldn't he go and sign the Paris agreement? That's an appropriate move for a Canadian prime minister that has prioritized climate change and said he's going to do something about it. An absence would have been remarkable."

VanNijnatten — who teaches courses on Canada-U.S. politics — said the frequency of Trudeau's trips to the U.S. in the last two months weren't necessarily planned, but rather opportunities that popped up.

President Barack Obama and first lady Michelle Obama pose for a photo with Prime Minister Justin Trudeau and Sophie Grégoire-Trudeau at the White House in Washington on Thursday, March 10, 2016, as they arrive for a state dinner.

"I think [people] should expect him to be on the road a little bit because he needs to show that Canada is willing to engage again," she said. "The kinds of issues that we face right now globally are not solved by Canada focusing on its own backyard, right?"

For Brian Bow, an associate professor at Dalhousie University who specializes in Canada-U.S. politics, the trips have been about shaping the image of a new government with a new prime minister.

"[The government wants] to cement the idea in Canadian voters' minds of [Trudeau] as sort of a statesman and an important figure and someone to be taken seriously," he told CBC News.

"There's such a conspicuous difference in the amount of time and the amount of attention that the new government seems to be putting into this compared to the previous one."

Though no immediate plans for another trip to the U.S. have been announced, Bow says to expect many more.

"The more time you are out there doing those international meetings, the more it kind of builds up your credibility as a leader at home."