BEIJING — As trade tensions with China escalate, President Trump has found new appeal in a regional trade pact he once called a “rape of our country.”

The pact’s members — including some of America’s most stalwart allies — might not make it so easy to come back.

Officials in Japan, Australia and New Zealand reacted coolly on Friday to Mr. Trump’s remarks that he would be interested in joining the Trans-Pacific Partnership after rejecting it so publicly just a year ago. While the United States would significantly bolster the pact if it signed up, its entry would require intense negotiations — and current members will expect significant concessions from the American side.

Comparing the multicountry trade agreement to “a glasswork,” Yoshihide Suga, Japan’s chief cabinet secretary, cautioned against any efforts to change it to accommodate Mr. Trump.