Senior Liberals are suggesting the federal Conservatives' cross-border campaign against the Trudeau government's $10.5-million payout to Omar Khadr could affect trade talks with the Trump administration.

Environment Minister Catherine McKenna and Prime Minister Justin Trudeau's principal secretary, Gerald Butts, both used social media to connect the Conservatives' condemnation of the Khadr payment with the renegotiation of the North American free-trade agreement, set to start on Aug. 16 in Washington.

The Conservatives, however, say any backlash in the United States resulting from the apology and settlement with Mr. Khadr, a former inmate at the U.S. detention facility in Guantanamo Bay, Cuba, is Mr. Trudeau's responsibility.

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"The fact that the Prime Minister elected to make this decision just as we were heading into NAFTA – that is his decision," Conservative MP Michelle Rempel, who appeared on Fox News this week to lambaste the government, said in an interview. The bickering between parties has strained the recent bipartisan co-operation on the Canada-U.S. file. In response to a question on Wednesday about releasing Canada's objectives in advance of the NAFTA negotiations, Mr. Trudeau told reporters, "I believe that the relationship with the United States needs to go beyond partisanship."

"I have been pleased that, up until recently anyway, we have been working very, very collaboratively and speaking with different voices but the same themes to the United States, to present a common front," he said at a news conference in Quebec City. He added he would be "more than happy" to meet with the opposition parties to discuss the government's approach to renegotiating NAFTA.

In a series of tweets Tuesday evening and Wednesday morning, Liberals and Conservatives blamed each other for any potential conflicts on the trade file.

"US announces NAFTA goals & #CPC MPs in US talking...Khadr w #altfacts. Irresponsible. Millions of Cdn jobs at stake," Ms. McKenna tweeted.

"Dangerous game #CPC is playing. Cda-US relationship should be above domestic politics. We should all be on the same team focused on trade," she later wrote.

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In a tweet, Conservative MP Candice Bergen told Ms. McKenna that the Liberal government "should have counted the full cost of your payment to Khadr. Not just in $$ but in potential damage to US/Canada [relations.]" Ms. McKenna responded that "NAFTA negotiations are about to start. Assume your party cares about Cdn economy & jobs. That is what you should be talking about in the U.S."

Mr. Butts also remarked on the timing of the Conservatives' criticism of the payment and apology to Mr. Khadr, a Canadian citizen who was sent to Guantanamo Bay at the age of 15 after he was accused of throwing a grenade that killed U.S. army medic Sergeant Christopher Speer and injured Sergeant Layne Morris in Afghanistan. The Supreme Court of Canada ruled in 2010 that the actions of Canadian officials who participated in U.S. interrogations of Mr. Khadr had offended "the most basic Canadian standards about the treatment of detained youth suspects."

"Conservatives mount aggressive anti-PM Trudeau campaign in the US, on the eve of NAFTA re-negotiation," Mr. Butts tweeted on Wednesday. On Sunday, the Wall Street Journal published an opinion piece from Conservative MP Peter Kent, called "A Terrorist's Big Payday, Courtesy of Trudeau," and Ms. Rempel appeared Monday on Fox News, the same day the U.S. administration released its sweeping list of more than 100 negotiating objectives for NAFTA. The Conservative Party also launched a website, "Khadr Questions," which invites visitors to tweet to Mr. Trudeau's government with questions and concerns about the payment. The site collects personal data from visitors, although a Conservative spokesman said it is not a fundraising initiative.

Ms. Rempel, who is in Washington for meetings this week, called the suggestion that the Conservatives' opposition is souring Canada-U.S. relations "absolutely ridiculous."

"Of course the Americans are going to pay attention to this issue, because it affects the families of the soldiers who were injured and killed," she said, adding, "A lot of Canadians don't share the Prime Minister's sentiment." Ms. Rempel added it is an indisputable fact that no court ruling compelled the Trudeau government to pay Mr. Khadr $10.5-million. "I think it was very important to clarify that this wasn't a payment that was dictated by a court."

Mr. Khadr's lawyers had filed a $20-million lawsuit against the federal government. Mr. Trudeau recently said he understands why Canadians are angry about the payout, but insisted a court case would have ended up costing taxpayers tens of millions of dollars more. The Liberal government has faced a public backlash against the apology and payment, with a public-opinion survey showing 71 per cent of Canadians opposed the deal.

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Mr. Khadr, now 30, spent more than 10 years in U.S. and Canadian custody, much of that time in Guantanamo. Once the youngest detainee there, he was transferred to Canada in 2012 after accepting a plea deal. He later recanted.

Ms. McKenna's office declined an interview request, but she recently sent a letter to her constituents in Ottawa Centre about her government's decision. She said legal actions relating to Mr. Khadr's case already cost the government $5-million.

"Our Government is committed to upholding the Canadian Charter of Rights and Freedoms. We benefit from having a Charter and it is of high importance that we ensure that the rights within it are upheld for all Canadians," she wrote.

She added the settlement agreement has no direct effect on Mr. Khadr's bail conditions or his convictions under the U.S. Military Commission Act.