Jim Webb is a serious man. A decorated military veteran, a talented author, a former secretary of the Navy and U.S. senator, someone who was right on Iraq when Hillary Clinton was wrong. But that's not the same thing as being a serious presidential candidate.
Webb announced that he was getting into the race for the Democratic nomination the afternoon before a summer holiday weekend, as people were heading home and going on vacation. That's a news dump, the way politicians bury unflattering news, not an announcement.
At a time when Strom Thurmond's son, a Republican state lawmaker, is calling for the Confederate flag to come down in South Carolina (his father had supported the compromise that moved it to its current location), Webb is still whistling Dixie.
Webb deserves a certain amount of credit for having the integrity to stick to his guns, something he didn't do enough as a senator, but there's not much of a constituency for this in the 2016 Democratic primaries. Any successful challenger to Hillary Clinton will have to win over a large number of black voters, which will be difficult to do when Webb isn't willing to go as far as NASCAR on the flag.