It happens by progressively showing strength of the party platform that a continued shift away from conservative bs is electable. The last few years has been powerful in continuing that trend after Biden was elected. Overturning women’s rights has blown up in republicans faces. Their hyped red wave a couple years ago turned out to be bs. A large number, not enough, but still a large number of gerrymandered maps have been overturned in courts after years of lawsuits, with additional ones still actively being fought in courts around the US. There are real progressive democrats dedicating their lives to fighting this stuff. If the trend continues to show that progressives will start taking control of the elections and safeguard democracy the progressive shift will show that a platform foundation exists for representatives to support those platforms. Without it they are stuck relying on independent voters filling the gaps and trying to bridge the gap between liberal and conservative enough that they secure as many independents as possible and come out ahead. Their isn’t enough strict support on the Democratic side to get elected as an ideal candidate and it’s not going to get there in a single cycle but we are four years into wins year over year and my personal opinion is if Biden wins handily and the house and senate make major strides this year it will not only enable more effective changes in policy, even though I feel Biden has far exceeded expectations, it will largely be due to disadvantage and youth voters and start to show that portion of the population as a more reliable vote to run a platform on which could be the beginning of a radical shift in how this country is run, in a good way. The liberal voter base needs a reliable foundation in order to support policies that folks like to bitch about otherwise your going to get politicians that have to try catering to the independent voter base and republicans as the only ones holding office.