Social democracy is a natural evolution of liberalism. Robespierre was a laissez-faire constitutionalist until the advances of the hungry mobs who allied with him because his liberalism was less willing to shoot them down than the reaction’s conservatism; then he rode their anger into power with the connivance of the business community who needed his help to deal with the national betrayal by the conservatives who would rather see France in the hands of Austria and Britain than liberals. Lincoln was a classical liberal until he needed the help of the radical left to break the power of the illiberal planter class and embarked on a radical redistributionist policy rather than let the much more dictatorial alternative take root. Franklin Roosevelt was elected on a platform of a balanced budget and a smaller government, but had to ally with the Communist Party (up to their usual Stalinist game of looking for ways to make deals with the capitalists at the expense of communism, but give the workers just enough to keep them under their leadership, i.e., more liberalism, in essence) and the CIO so that communists wouldn’t take over the country.
The consistent thing about classical liberalism and modern liberalism is looking out for the capitalist class and being willing to break with tradition, and compromise with forces with their own agenda ... to a point ... to do it. It has always meant freedom for the few and repression for the many.