For a variety of reasons, including globalization, demographic change, and slow growth, inflation and interest rates were extremely low between 2008 and 2021. The Democrats could consequently contemplate dramatic expansions to the welfare state and corresponding increases in the deficit without worrying much about the bond market.
Times have changed. As a result, any progressive running in 2028 will have to deal in tradeoffs. If the Democrats want to overthrow the dollar store economy in the foreseeable future, they will have to propose large tax increases, and not just for the extremely wealthy, to make their plans credible.
If I had to guess today, I would say that won’t happen. The intellectual battle between the center and the left in 2028 will pit plans for very small changes to the welfare state, accompanied by tax increases solely on plutocrats, against sweeping progressive proposals which dishonestly assume the plutocrats can pay for everything. Tax increases on the middle class will just be too much for the electorate to swallow.