The two men I believe have the best chance at the Harris VP slot are Julián Castro from Texas and Rep. Tim Ryan of Ohio. Both are currently running for the presidential nomination, but are they doing enough to merit second place consideration?

Castro is the top choice of only 1.3% of Democratic primary voters, according to the RealClearPolitics poll average, while Ryan fares even worse at 0.1%.

But popularity with primary season voters – or even widespread name identification at VP selection time – is not often a factor. (See Gov. Sarah Palin and Sen. Joe Biden in 2008 and Gov. Mike Pence in 2016.) Instead, what matters most in the modern era are the constituencies a candidate can bring to the ticket or help boost a perceived weakness with the presidential nominee.