To say that Ms. Maddow didn't think much of the idea would be a bit of an understatement. There was also more than a trace of disappointment that the idea originated with Bernie Sanders himself.

RACHEL MADDOW: On the day the Republican Party frontrunner clinches the nomination, an absolutely, 100% unprecedented plan now, to debate head-to-head, one-on-one, a candidate from the other party who, honestly, is not really in contention to win his party’s nomination. This is very strange. This is unprecedented.

Of course, strategically from Donald Trump’s perspective, this is like a hat trick and a grand slam and a slam dunk all in one. There’s no downside for Donald Trump to doing this, there’s no risk…Imagine the worst-case scenario for his debate with Bernie Sanders, where Bernie Sanders just trounces Donald Trump…That also poses no long-term strategic risk to Donald Trump, because there is no chance that Bernie Sanders is going to be Donald Trump’s general election opponent.

And, in fact, the better Bernie Sanders looks in a debate with Donald Trump, the better it is in the long run for Donald Trump, because that would only elevate Bernie Sanders’ standing in the ongoing Democratic primary…And if you elevate Bernie Sanders’ standing in that primary, which Bernie Sanders has no chance of winning, that still prolongs that already-long and expensive primary. It further undermines Hillary Clinton’s standing as the Democratic likely nominee…It only undercuts her. I mean, for Donald Trump, this prospect of a debate with Bernie Sanders all upside — all upside for him. Why on EARTH would Democrats let him play in their primary like this?

Maddow later compared the idea to President Obama debating Newt Gingrich in 2012, and admonished Sanders for ignoring his real opponent in the Democratic primary.

Update (Karoli): Trump says nevermind, no debate after all.

Trump says in a very Trumpian statement that he won't debate Bernie Sanders. pic.twitter.com/O6arGwPd8f

— Sahil Kapur (@sahilkapur) May 27, 2016