A North Korean envoy is coming to Washington bearing a letter for President Donald Trump from Kim Jong Un.

This has been going on for days. Like in the old days.

Kim Yong Chol was spotted Wednesday at Beijing’s airport, where he boarded a commercial flight to the US.

On Thursday, he met Secretary of State Mike Pompeo in New York. Now it’s on to Washington, still carrying that letter, which in some fashion is a response to a letter Trump dictated for Kim.

The fate of a historic US-North Korea summit may rest on what’s in Kim’s letter.

And it’s all unfolding at the speed of pen pals.

Opportunities abound in the digital world for immediacy in communications, as everyone knows and Trump demonstrates with every tweet. Also, the telephone has been around for a very long time.

But still there’s a whiff of the Pony Express, Western Union and the flourish of quill pens in diplomacy.

“Some of it is the ceremony,” said Princeton presidential historian Julian E. Zelizer. “There is a drama to delivering a letter that I think still serves the purpose of two countries slowly trying to work things out.”

And letters can be a useful medium for tempestuous leaders like these two, he said. “It’s a way to contain emotions. Some of the coldness of the letter can be good in diplomacy.”

Major diplomatic actions are often communicated on paper, even now, for the sake of formality and posterity. That’s especially true for messages between countries that do not have close ties and thus aren’t used to communicating with each other regularly through more informal means.

President Barack Obama and Iran’s Ayatollah Ali Khamenei famously exchanged secret letters in 2014, for example, in the run-up to the nuclear deal negotiations.

Trump’s letter to Kim announced the summit was off because of harsh rhetoric coming from North Korea, yet it contained the seeds of reviving the idea. Most recently Trump has exhibited an air of anticipation about the envoy’s journey to Washington.

“I believe they will be coming down to Washington on Friday,” he told reporters at Joint Base Andrews before departing on Thursday on a trip to Texas. “A letter being delivered to me from Kim Jong Un. It is very important to them.”

In the normally buttoned-down world of diplomacy, letters often contain information that has already been conveyed by other means. The chance of a breakthrough being revealed in a hand-delivered note from across the seas is remote.

But Kim and Trump are not buttoned-down people, so bets are off.

“If there ever was a moment that a president does not know what is coming,” Zelizer said, “this is that moment.”