Tom Shannon retired from the State Department in June after a 34-year-career that propelled him to the third-highest ranking official — and a short stint as acting Secretary of State. The decision to leave, he said, was entirely personal.

But in his first interview since his retirement, Shannon told VICE News thatt he strongly disagreed with some aspects of the administration’s policies — namely, on the border wall and immigration.

“We can't close the border,” Shannon said. “We have over a million people cross that border everyday legally. And we have more than a billion dollars of goods and services come across that border every day and because of the North American Free Trade Agreement we have built an economy along the frontier."

"So attempting to close the frontier is a fantasy," he added. "It doesn't work." He also called family separations “dramatic and cruel.”

When Shannon retired, he was widely viewed as the elder statesman of the department, someone who had served under six presidents and 11 secretaries of state. Rex Tillerson, President Donald Trump’s first secretary of state, referred to Shannon as a “walking encyclopedia” of the place. His career began with postings at embassies in Africa and, especially, South and Central America.

READ: Here’s what Trump’s Helsinki speech could mean for America’s standing in the world

Despite the challenges brought on by the Trump administration, Shannon rejected much-circulated reports that morale at the State Department had reached a low point by the time he left.

“There's a joke in the State Department, which is that morale is always as bad as it's ever been,” he said. “There is a larger issue at stake here which is not the president. It is the kinds of changes that are taking place in the world, but especially the kinds of changes that are taking place within the United States."

As a career diplomat, Shannon said, working for administrations he disagreed with just came with the job. “This is really what's required of us as civil servants, whether it be foreign service officers or civil servants,” he said. “We have taken an oath to serve our elected leadership and to protect our Constitution.”

“If for whatever reason we find ourselves in a position which we cannot, then we have to leave," he continued. "And that is the honorable thing to do.”

Correction: Due to a transcription error, one of Tom Shannon's quotes was rendered incorrectly. The quote has been corrected.