It's pointless to separate out "FDR's policies" from "WW2". Both are massive gov't spending, the same Keynesian stimulus at heart for an under performing low-demand economy. Gov't spending, whether it's schools, highways, police, or blowing shit up with the military is all still gov't spending.
Also, FDR's policies got us involved in WW2 as soon as possible, so one leads to the other: FDR's policies -> WW2. He was fighting huge internal opposition against involvement, i.e. Conservative isolationist movement. Nonetheless we supplied Britain with food and war materials long before the Pearl Harbor attack effectively smashed down the right wing isolationists from further influence, alongside pro-Nazi sympathizers as well.
Funny, they never really went away did they? Trump brought that zombie out of the dungeon.
So much to be proud of there.
The massive WW2 spending surge put everyone to work, but other sorts of spending would do just as well (better in fact, since you get infrastructure out of it) -- look at post-WW2 Japan, Germany, or Costa Rica. Tiny to non-existent military, yet robust growth. Costa Rica in particular puts all its neighbors to shame. You do not need military spending for economic growth, although it can be an "easy mode" political solution when you have anti-gov't spending conservatives who somehow think massive military budgets are "ok" but nothing else.
FDR and his New Deal gave us the Middle Class.
Without his policies we'd still have Gilded Age oligarchic control of the economy, most people living in piss poor working class conditions, trailer parks, ghettos, etc... what the oligarchs are trying to bring back for us today. The golden age of middle class America was the 30's - 70's, each generation living much better than the one before. It's been eroding ever since. That gap between the lines in the graph is wealth that has been siphoned off nearly all wage-earners into the pockets of corporate ownership. The balance shifted, hence no more golden age.
It's common for Liberals to blame Reagan for starting this trend -- and he certainly contributed mightily -- but it actually began in the early 70's, a decade before him and a product of much larger political forces than just one president or even one party.
I have trouble seeing much similarity between FDR and Trump... that's a real reach. But Trump
does (or did?) want to push through a massive $1 trillion infrastructure bill, and that's FDR-style socialist gov't expenditure all the way, for sure.
You think the GOP will ever allow him to do it though? They had two years of full control (before losing the House in '18) and I only saw Trump get swatted down.