What happened to the Democratic Party since ~2000?

I grew up in the 90s in a Democrat household, and it seemed like up until the 2000s, the Democratic Party in the U.S. was a lot more unified as far as being able to rally voters around candidates and specifically didn’t have so many issues marketing presidential candidates. It also feels like both Dem presidents and representative majorities would get more done while in office. Was that just my perception as a kid? If not, what has happened since to lead to more challenges with Dems getting into office, as well as Dems in power seeming more ineffective? OR is it just public perception or media coverage that they are both less productive in office and harder to elect?