The latest: Former Pennsylvania congressman Joe Sestak announced Sunday that he's running.
The Dem-on-Dem attacks have begun
The niceties have ended: 2020 Democrats are breaking their own pledge not to go after one another. The attacks of the past week show what a long primary they're in for.
Why it matters: These jabs and skirmishes show a fracturing Democratic Party — exactly what some top Democrats wanted to avoid in order to maximize their chances of defeating President Trump.