The FDR coalition was built at a time of near-revolution in the country. You cannot look at that time without realizing the powerful strikes and left-socialist agitation that was going on. While the sit-down strikes that unionized the auto industry and the Teamsters strike that paralyzed my home town of Minneapolis happened after FDR was elected, they were also the outgrowth of years of socialist organizing.
The Farmer-Labor and Progressive parties at state levels made a big difference in presidential politics. The Populists controlled NEBRASKA (!!) a few decades earlier. Socialists got into the Perot territory of votes in general elections.
The Democrats got where they were by co-opting that message. FDR, after saving the banks, instituted social-democratic policies. Even though their economic policies were demonstrably bringing the whole ship down, the big capitalists of FDR's day fought tooth and nail against him. But he was bringing the Red Bear of America to heel; enough of the ruling class aquiesced, AND FDR's policies were actually socialist enough to make a difference in the lives of people.
Those who say they want to bring together FDR's coalition through re-framing and massaging the message, without dealing with the fact that the Democrats have gotten into bed, in important policy ways, with corporate capitalism, are missing the point. If you don't deliver real goods to real people they'll split on you.
Truman was an intentional choice to be next president - that's why New Dealer Wallace was dropped from VP in 40 to off the ticket. They knew FDR wouldn't survive the term; the anti-New Deal parts of the Dems picked Harry S to be their boy.
The article also skips over the second Red Scare. Wallace, that pro-socialist, was running on defense of the New Deal. The veer to the right that McCarthyism was gave us the Taft-Hartly act, which gutted labor power. It gave us interventions in Central and Southern America, Korea, and the purging of socialists - who were focused on reigning in money power and delivering goods to people - from the Democratic party.
Short version: can't rebuild FDR without telling corporations to take a hike.
FDR certainly took advantage of the progressive movement but the huge electoral block was also built on reuniting southern and northern democrats - a bridge that may no longer be able to be crossed.
I am not sure I understand the last few paragraphs - Truman vetoed the Taft-Hartley Act, his policies were described at the time as "a grab bag of well worn New Deal ideas", and routinely sttacked the "gluttons of power" and "Wall Street reactionaires" (his words). McCarthyism didn't start until Truman's second term, post election. The distinction between Wallace, who favored socialism, and Truman is more than what you describe.
As for Truman not being a New Dealer - his Senate record shows otherwise. He voted with Roosevelt on every piece of legislation, except possiblely expansion of the court, and was routinely mocked in Missouri as a New Deal "yes-man" so much so that he faced a serious challange to re-election to his senate seat in 1940.
