A leading U.S. Republican senator on Tuesday urged allies Australia and Japan to continue to move forward with the Trans-Pacific Partnership free trade negotiations, despite the U.S. withdrawal,

“I know Australia is now talking with Japan and others about moving forward with TPP despite America’s withdrawal. I would strongly encourage that,” Sen. John McCain said in a speech in Sydney.

“The case for an open, rules-based, regional economic architecture is just as compelling today as it ever was. So I would urge you to keep at it. And hopefully, someday in the future, under different circumstances, America will decide to join you,” he said.

The Senate Armed Services Committee chairman slammed U.S. President Donald Trump’s decision soon after taking office in January to withdraw from the TPP as “serious mistake.”

He has argued that the move has damaged the strategic position of the United States in the Asia-Pacific region and will have lasting consequences for its economy.

“The fact that both American presidential candidates last year opposed TPP, and America’s subsequent withdrawal from it, was a major strategic mistake,” McCain reiterated in his speech at The United States Studies Center, located at the University of Sydney.

Since the U.S withdrawal, the remaining 11 signatories are at odds over whether to move ahead with realizing a TPP without the United States.

Australia, Japan and New Zealand advocate a quick implementation of the deal without the United States, but other members appear reluctant. The TPP, signed in February 2016, also includes Brunei, Canada, Chile, Malaysia, Mexico, Peru, Singapore and Vietnam.

McCain, who is briefly visiting Australia before heading to Singapore’s Shangri-La Dialogue for regional security talks, used his speech to reassure Australians that despite “understandable” doubts and concerns about where the United States is headed under Trump’s leadership, his country “stands by our allies.”

“I realize that some of President Trump’s actions and statements have unsettled America’s friends. They have unsettled many Americans as well,” he said.

“Now more than ever, we Americans are counting on Australia and our other allies to stick with us … to encourage us to stay true to who we are at our best … and to remind us always just how much is at stake,” he said.”