The ideal candidate as I imagine would be:
White man between 50 and 65, about 6ft 4in tall, two-term governor of a large state, previous experience in the House and/or the State Legislature, charismatic and very good speaker. Compassionate family man, but image of a tough guy when it comes to dealing with opponents and foreign advisories. And somebody who drives Trump crazy and lets him look like a fool when he tries to attack the candidate. However, candidate has to have a good sense of humor of course and, despite having a wide knowledge on all major issues, not the image of a technocrat.
Socially liberal, moderate on guns, focuses on balancing budgets and making government more efficient. Supports green energy, but doesn't want to shut coal immediately down and offers training programs to coal workers to find new jobs. Supports a higher minimum wage and single-payer healthcare. Also focusses on campaign finance reform (maybe something done as governor already). Moderate pro-free trade, supports a 15$ minimum wage and pro-choice.
$15 minimum wage and single payer are toxic to the american electorate.
