He's 38... no President has been under 42 (Teddy Roosevelt).
He has no experience... being the executive over a medium college town (Notre Dame), mostly presiding over city parks and roundabouts.
He has no idea how to deal with race issues... he has given a deer-in-the-headlights response twice to race-baiters from the Left accusing him of not being good to blacks in South Bend...
Simply put, even the Left knows that he is "not ready for prime time", Let him win Governor of Indiana and be successful there for a decade, and then maybe he could have a claim to lead the free world... but I don't see either one happening.