Well, it IS a political "holiday", and that particular episode seems to be aired exclusively on political holidays, such as Memorial Day, or occasionally Labor Day.

Both of the entries in this episode are very enjoyable, I like the imagine spots sprinkled throughout both, such as Arthur's fantasies about meeting the president, the president asking for his help in redesigning Washington, he and the president becoming pals (all of which I'm sure some  kids have had), and even D.W. writing new laws since she got loose in the White House. There are also a number of subtle humorous moments throughout "D.W. Goes to Washington" as well: "How can you share a sundae with Santa when you don't bring a sundae TO Santa", or the Secret Service trying to locate D.W. ("Who lost a duck?").

Likewise, the imagine spots in "Arthur's Mystery Envelope" are funny too, I wonder what when through that China girl's mind when she found a note from Principal Haney, "EWW!!!" Or him trying to hide the envelope, and it just keeps getting bigger and bigger until it breaks through the entire house. You have to admit, this would be a relatable scenario for kids... I don't remember if I ever went through a similar situation, but I can imagine a kid would be freaked out if the principal gives a big envelope to give to their parents, and not knowing what the contents are.

It was very refreshing to see this episode today.