Let’s begin with the obvious: No Democrat has won a statewide race in South Carolina since 2006.

That includes nationally recognizable names like Bakari Sellers, the former state legislator who ran unsuccessfully for lieutenant governor and is now a CNN commentator, and moderates like James Smith Jr., who lost his race for governor last year to the Republican incumbent, Gov. Henry McMaster.

Enter Jaime Harrison.

Mr. Harrison, the first black chairman of the South Carolina Democratic Party and a former Washington lobbyist, declared his candidacy on Wednesday morning for the U.S. Senate seat held by Lindsey Graham, a Republican who has served three terms. Mr. Graham’s race is likely to draw attention in 2020: He has shifted from a sharp critic of President Trump to a prominent ally, and Democrats are hoping that grass-roots energy around defeating Mr. Trump will help some Senate and House candidates score unlikely victories. (Mr. Trump carried South Carolina by 14 percentage points in 2016, of course.)

In an interview with The Times in New York City, Mr. Harrison — who stepped down as state party chair in 2017 — discussed the difference between a conservative and a Republican (in his view), the 2020 Democratic presidential race, and why he believes some South Carolinians will punish Mr. Graham for his embrace of Mr. Trump.

This interview has been condensed and edited.

Q: How can a Democrat win statewide in South Carolina?

A: If a Democrat runs the race I’m going to run, which is not about Democrat or Republican, or is not about left or right, but is about right or wrong — if a Democrat runs that type of race? They can win.