It depends on what time frame you're referring to.
You set the stage with FDR.
Call it the 20th century.
I would say that liberals held the upper hand from FDR to LBJ. Nixon was also a Keynesian, so he clearly had some liberal influences. That's when they saved capitalism.
I called Nixon a commie back in the day.
Imagine taking control of government, & demanding that
no pay or price increases are legal without Nixon's stamp.
Nixon was the perfect liberal...economic authoritarianism,
feting communist China, waging that useless war in Vietnam,
But once Reaganomics came into the picture, the liberals were all but defeated and powerless, especially on economic issues. Their only hope to remain political relevant was in embracing identity politics, a strategy which worked for a while but now showing diminishing returns.
Isn't it odd....liberals give Presidents credit when they're
Democrats, & things improve. But when the Jimmy Carter
Malaise ended under Reagan, no credit at all.
So, basically, what we have now are conservative capitalists and limousine liberals on the same side, with the extremists on the nationalist right growing in power. The socialist left is weak and politically impotent, as exemplified by the dismal failures of Occupy Wall Street and the widespread opposition to Sanders from the Democratic (liberal) rank and file.
Liberals....they love regulation, high taxes, war, limiting speech,
the prison system, civil forfeiture, war, racial quotas, & war.
As long as blacks don't move into their neighborhood, they're
happy as clams. Conservatives are no better. And Libertarians
are useless. We're all doomed.