The “mouth” and the “kid” in Vegas……

According to Donald J. Trump, Senator Marco Rubio of Florida is “just a kid” — too young and too inexperienced to be taken seriously as a presidential candidate. But what if Mr. Rubio were to be the one who comes out of the spat looking like the grown-up?

We may begin to get an answer to that on Thursday as both men travel to Las Vegas to campaign in events just a few hours apart. Mr. Trump will hold his rally first on the Las Vegas Strip at a theater that, perhaps fittingly, is home to an installment of the theatrical and grandiose Cirque du Soleil series. It is hard to imagine he won’t take more shots at Mr. Rubio, who has been the subject of Mr. Trump’s constant needling and taunting for the last few weeks.

Mr. Rubio will appear later to speak to supporters at an affluent development of west of the Strip. Don’t expect him to say much about Mr. Trump. He hasn’t been taking the bait so far, believing that avoiding the back-and-forth would give him the higher ground. And that of course helps Mr. Rubio, 44, appear to be something he isn’t often called in a presidential field of older, more seasoned politicians: the adult.