It doesn’t require the handful of swing states to be onboard. It just requires the heavy hitters which are largely marginalized by the electoral college and some of the smaller deep left or right states which are also made pretty irrelevant in terms of campaigning even if they get a bit more influence
Depends on what definition you use, classically a social Democrat is someone who believes in using democratic means to gradually and peacefully transition from capitalism to socialism. The definition you are using is actually closer to a social liberal but even that isn’t quite right, welfare does not imply a mixed market economy on its own, welfare can exist in a pure laissez fair market economy. Social liberalism is in favor a mixed market economy which is a further step left from simply a regulated market economy with welfare. In a mixed market economy key industries are publicized and owned and operated by the government for the public benefit while allowing for the possibility of private competition as well as an open market economy in other industries and areas.