There is no context to the tweet. On his timeline it falls in between a picture of him snuggling Martin Short on a couch and a sarcastic jab at the media's fixation on the firing of New York Times editor Jill Abramson.
I look forward to the creative Wheel of Fortune jokes we'll see over the next couple of days, you unpatriotic racist bastards.
Update: He might not have meant it...maybe? Sajak is well-known for his conservative political views, so it's hard to tell anymore in a day and age where reality regularly laps satire.