President-elect Donald Trump’s controversial phone call with Taiwan’s president on Friday was the work of Trump staffers and Taiwan specialists that had been months in the making,The Washington Post reported, citing sources familiar with the matter.

Stephen Yates, a national security official under President George W. Bush, told the Post that Taiwan was on the Trump transition team’s list of foreign leaders to reach out to “very early on.”

“Once the call was scheduled, I was told that there was a briefing for President-elect Trump,” Yates said. “They knew that there would be reaction and potential blowback.”

Taiwanese media reported late Friday that Trump’s team had arranged the call with President Tsai Ing-wen. A spokesman for Tsai,  meanwhile, told Reuters over the weekend that  “of course both sides agreed ahead of time before making contact.”

The Post report and the spokesman’s statement appear to differ from the Trump team’s explanation for the call, which Vice President-elect Mike Pence on Sunday said was “nothing more than a courtesy call.”

Pence told ABC on Sunday that Trump “took the call, accepted her congratulations and good wishes and it was precisely that.”

Read the whole story from Business Insider.