Liberal MP Leona Alleslev surprised many in announcing in the House of Commons on Monday that she was crossing the floor to join the Conservatives.
"Purchasing used CF-18s from the Australians will not give us capability, will be cost prohibitive, and frankly, humiliating when we should be reassuring our allies in a time of unprecedented global instability". "She will be a strong asset in our growing Conservative team as we work toward 2019".
Trudeau said little about Alleslev's move.
Alleslev said she felt the Conservatives were more "focused on those fundamental challenges" than the party she had left.
She said their government needs to be challenged openly and publicly and she didn't feel it was possible for her to do that while remaining in the Liberal caucus.
"That's a hard decision and one that everyone really needs to make, I think, on their own".
The 50-year-old Alleslev is a bona fide score for the Conservatives, and her departure a huge blow to the Liberals.
"Leona made it clear that the direction that this government is headed under this current prime minister, under Justin Trudeau, is not the necessary leadership that we need as Canadians to deal with the very serious issues that are facing this country", Mr. Scheer said.
Democratic Institutions Minister Karina Gould said Alleslev, like other MPs, has the right to change her opinion, and that citizens will have their say on any political switches during next year's federal election.
"A country, its sovereignty and (its) values are fragile", said Alleslev. He suggested neither will be an easy task in negotiations with the mercurial Trump.
Alleslev seemed to back up her former colleagues on Tuesday, suggesting her choice may not reflect greater turbulence within the Liberal ranks.
Rookie MP Leona Alleslev, elected in the new Ontario riding of Aurora-Oak Ridges-Richmond Hill after defeating the Tory incumbent, was immediately tapped by Scheer to take on a key role in caucus as the party's critic of Global Security.
She has a business background as a senior manager at Bombardier Aerospace and IBM, and also served as captain in the Royal Canadian Air Force.
As an MP, she has served on the immigration and defence committees and as chair of the Canadian NATO Parliamentary Association. Former Conservative MP Maxime Bernier, who recently created a new party, was sitting far from his former colleagues with Green Party Leader Elizabeth May.