A new letter to President Trump from North Korea’s Kim Jong Un has reinforced the cordial relationship between the two leaders and kept the door open for another summit meeting, which Mr. Trump suggested might happen soon.

“Thank you to Chairman Kim Jong Un for keeping your word & starting the process of sending home the remains of our great and beloved missing fallen!” Mr. Trump wrote on Twitter, referring to what are believed to be the remains of U.S. soldiers killed in the Korean War. “Also, thank you for your nice letter...