If he blows this opportunity, he will have a short-lived two year run before Senate leadership changes again. If there's one thing a politician wants above all else, it's to remain in power.
Don't screw this up, Mitch!!
Even if there are more ‘pub seats up, so what? If they just keep the ones they have, they break even. It’s up to the Republicans in the US Senate to clean up the mess, or they will lose their majority, and probably the presidency.