It's too bad to see John Hickenlooper drop out of the Presidential race. Whatever you might have thought of his policy positions, he was one of only a few candidates in the running with experience as a governor. Now, only Jay Inslee (of Washington) and Steve Bullock (of Montana) remain among the Democrats. (Bill Weld, challenging the incumbent President for the Republican nomination, is also an experienced governor.)
Aside from all of my other complaints with how we treat the modern Presidency, my most important concern is that the job go to people who have practice in the next-closest thing. Flying a Boeing 747 is a different skill than flying a Canadair CRJ-900 regional jet, but it's a whole lot closer than driving a truck. Being a governor isn't the same as being President, but it's mostly a difference of scale, not of form. (Bill DeBlasio and Julian Castro each deserve partial credit for experience as mayors of very large cities -- but even then, governors have Presidency-like duties like leading the National Guard units of their states that mayors do not.)
Like Presidents, governors have to work with legislators and judges. Governors have to oversee legions of public employees and manage budgets. Governors have to satisfy public demand for a figurehead (literally acting as a state's head of state), and they have to step up and take responsibility when things go wrong under their watch.
Most importantly, governors have to develop teams of trusted advisers and staff members who can help them to respond effectively and responsibly to the unexpected. Americans today expect our Presidents to enter the Oval Office with big dreams of what they'll achieve in their first 100 days. But the reality is that what's most important isn't what a President wants to do...what's most important is whether they're prepared to navigate the unexpected "3 a.m." challenges -- like 9/11, the 2008 financial panic, Hurricane Maria, or China moving troops into Hong Kong.
Practice doesn't always make perfect -- but practice can help us weed out those who don't have the right stuff for the bigger jobs. And the better the practice, the better we as voters should be able to expect. The Presidency shouldn't be about what the President wants to do -- it should be about the leader they're prepared to be.