What exactly is Tom Steyer planning to do?

Polls say the billionaire environmentalist is poised for a top-three finish in South Carolina. What that gets him is less clear.

As Democrats begin to lose patience with the size of their 2020 presidential primary field, one candidate could be poised to seize attention with an unexpected finish Saturday.

Tom Steyer, the California activist billionaire who has largely been a nonfactor in the primary campaign so far, is on track to finish in the top three in South Carolina's contest, according to recent polls, potentially depriving former Vice President Joe...