They didn't have those majorities for a long time. Runoff elections and deaths gave them a two month window or so. They passed Obamacare with that, and had to remove a single payer option to get the last necessary votes.

But also, the Democrat party was a lot less left in those days. There were a lot of Manchin types of conservative Democrats. We've never had the votes for electoral and ballot reform. We needed to build on our majority in 2010 to do it, and we instead we lost the majority entirely.

I’d say the RNC has had a hostile takeover that’s going to lead to a schism, versus an evolution. Post/Reaganism was an evolution that the RNC did very successfully co-opt. Trump’s populist rhetoric has been damaging to the status quo for vested interest, both political and corporate. The tea party movement fizzled out because Obama was popular and had majorities, so their impotent rage didn’t have a strong figurehead until Donnie in 2016.

I don’t see the progressives changing the party - see: Talib’s censure, Bernie being sidelined until late, or how intra-party caucuses like the squad or the black caucus falls in line. On the right where gridlock is a feature, the house freedom caucus can force an embarrassing number of speakership votes until their ultimatums are met, and be lauded as heroes. Progressives and their voter bloc want a progress, and so have to play ball with the DNC.

Remember that DoMA went away from a court case, not primary legislation. The ‘gay vote’ was seen as reliable by the DNC, because it’s not like the right is opening its arms to those voters, so there wasn’t any political capital spent on that issue. Just lip service all through the Obama majority years