By being uninspiring and boring and losing because of it.
Republicans promised a bulldozer the size of a small city and they're delivering. Sometimes people prefer winning even if it means they lose.
They went big and the Democrats went home, offering "sensible policy" and "reasonable governance" and programs for Pell Grant recipients who start a business that operates for three years in disadvantaged communities.
None of that is bad on its face but it doesn't win elections. Especially when Elon is promising a Sandals resort on Mars.
Even if you disagreed with Bernie, the guy was willing to go big and bold and cared about what he was promising. It doesn't have to be universal healthcare. It can be UBI or building a solarpunk future or colonizing the bottom of the ocean. The Space Race. The Great Society. Morning in America. The New Deal. Something big and exciting and someone we believe really, really wants it.
The Republicans are promising front row seats to the end of the world and the Democrats are promising to check everyone's tire pressure. Understanding why the former can appeal more than the latter is the key to winning future elections.