As Jon Stewart winds down a 16-year run at "The Daily Show," his frequent targets -- a long list of 'em -- have just eight more days for payback, which may explain why Texas senator and presidential hopeful Ted Cruz abruptly backed out of an appearance on the program Monday night. 

Reasons for the cancellation are unknown (Historian David McCullough appeared in his place) and no explanation was given -- votes needed to be taken, or something like that, Stewart briefly noted -- while an email query to the senator's office remains unanswered. 

Cancellations on "TDS" -- or any late night program -- are hardly unprecedented and do indeed happen, although not frequently. What makes this so unusual is twofold:

QuizQuiz: How well do you know the 2016 contenders?PhotosCelebrities who are Republican, conservativeMore coverageOpinion and analysis about the 2016 presidential campaign

Foremost, Cruz on "The Daily Show" is an incongruous match  -- the incongruity of which needs no explanation. 

Second, we are now in the final roundup for Stewart, whose legendary run ends Thursday, Aug. 6.  (No one canceled on David Letterman in the waning moments of his historic final lap...)  

There are possible reasons for the Cruz cancellation. He is in the midst of a battle with majority leader Mitch McConnell -- which erupted Sunday night on the floor of the Senate. In addition, Cruz -- who I believe has never visited the show -- has been a frequent target, of course. Cruz has been attempting to distance himself from the presidential-hopeful pack --  a growing one --  and while next Thursday's debate is intended to accomplish that, Monday's "TDS" appearance was doubtless part of the plan as well. The risks were obvious: Cruz may be an expert debater, but Stewart is an expert deflater. 

advertisement | advertise on newsday

Alas, it would have been fascinating television. 

Meanwhile, Donald Trump claims "TDS" has asked him to appear -- and that's almost certainly true. Why wouldn't Stewart want a final showdown. Trump has been a guest over the years, and a frequent target -- the soon-to-be-former "Daily Show" host feasting on his run (and hair) for weeks. Trump now has to ask himself whether the considerable risk outweighs the benefit: Leading in New Hampshire, the answer to that may be self-evident.