Conservative foreign affairs critic Erin O'Toole was sitting in the departure lounge at Reagan National Airport in Washington, D.C., last week when his eyes landed on a story he wasn't expecting.

"'Napping on NAFTA': Harper blasts Trudeau government handling of negotiations,"' read the headline on a Canadian Press story about a memo written by former Conservative prime minister Stephen Harper.

"What?" O'Toole recalled thinking. "Oh, dear."

Harper had shared gloomy thoughts on the deal a few weeks prior during an event in Washington, but the memo, which castigated the Liberals directly, was a rarity for an ex-political leader who has largely stayed away from any direct remarks on the current government since the 2015 federal election.

That the memo suddenly found its way into the public domain — he'd been writing them for months and none have ever surfaced — left political observers scratching their heads. Who would leak it? And why?

Prime Minister Justin Trudeau wouldn't directly address the letter or its potential implications when asked about it on Monday.

"I hold the office of prime minister in high regard, and because of that I hold former prime ministers in high regard, and will not make any comments on what he had to say."

Tories blindsided

O'Toole was sitting at the airport having just wound up a trip to D.C. with the House of Commons foreign affairs committee to advocate for Canada's interests at the NAFTA talks, part of an ongoing collaborative approach the Conservatives are trying to take to the negotiations.

Harper's letter took a swing at Canada's negotiating strategy, suggesting the Liberals were letting the Americans run all over them and putting the future of NAFTA in real danger.

Some Tories say quietly they suspect an attempt to harm the Conservative Opposition and undermine leader Andrew Scheer's efforts to make a break from the Harper era. The Liberals say Harper has jeopardized the talks by playing politics with the united front Canada is trying to put forward.

"I think he's got a grudge to hold and he's more interested in putting stuff out there that is going to do damage to our negotiating positions," Liberal MP Bob Nault, the chair of the committee, told CBC's "As It Happens."

The letter was written for clients of Harper's consulting business. Some Conservatives allowed that he ought to have known there was a risk it would become public, but say Harper's team never gave Scheer's office a heads up, suggesting it was never meant for broader dissemination.

Harper's tone

Not to mention a well-known fact about the former PM: he loathes leaks — so much so, in fact, that he once panicked when a staffer, Geoff Norquay, was forced to leave a meeting to deal with one, former Harper aide Bruce Carson recounted in his own newsletter this week.

"It took a while to settle Harper down and get him to understand these were leaks in Norquay's roof at home caused by ice dams that are symptomatic of the late winter in Ottawa," Carson wrote.

Rachel Curran, Harper's former policy director, said his consulting firm will take more care with his memos going forward. This one, she said, was a warning to the business community and was never meant to have political implications.

"His advice was framed as, 'Americans are going to insist on a better deal and are prepared to live with the political and economic risk of NAFTA collapse, get yourself ready,"' Curran said.

O'Toole said the positions Harper takes aren't so different from those the Opposition Conservatives have been trying to advance in Parliament, though Harper's tone may have been different.

"Certainly, when a former prime minister weighs in, someone that was well known for trade, it caused a bit more of a splash or ripples than when MP Erin O'Toole or someone like that weighs in," he said.

Team Canada

He said he doesn't feel the current strategy needs a reboot, adding that the Tories remain committed to working with the Liberal government to advance the talks.

"I've shared some of the concerns he's raised, but we're here — the current group of parliamentarians are here — to work with the government where we can."

International Trade Minister Francois-Philippe Champagne said Team Canada continues to play together on the NAFTA talks.

"You have to take it with a grain of salt," he said of the letter. "This is a comment from someone who is not at the table."