I can't agree with your assertions, particularly about Donald Dump "taking over the Republican Party" and Democrats standing back and letting him do it. The Republican Party gave up any claim to decency in January 2009, when it decided that thwarting the agenda of a black man was more important than being the "loyal opposition."
Republican members of the House amd Semate went out of their ways to demonstrate to their constituents how openly disrespectful they could be to President Obama. Their blatant actions showed to their followers that the racism they'd kept under wraps for years was not only appropriate, but also, encouraged, to display.
Dump didn't take over the Party in 2016. He was the figurehead on a ship that was already built. What he did do was to lower standard for integrity, competence, honesty, and morality. After eight years of being disrespectul nay-sayers since 2009, the public's standards and expectations for the behavior of "public servants" became so debased that they would accept anything.
The Democrats who are "so old" now, weren't quite as old 14 years ago. They had more vigor, perhaps, but the didnt have public backing. Too many people were too excited to let their hate flags fly. They weren't listening to Democrats then, and they're making excuses for Republicans' bad behavior now. It shouldn't take Democrats to claw Democracy back from the haters. It takes formerly reasonable Americans demanding decency from their Republican "leaders" and letting go of the gleeful hatred they have so enjoyed displaying for more than a decade.
I suppose we can blame people who, allegedly, "let something wrong happen." However, isn't it more appropriate to blame the ones doing wrong in the first place?