I don't buy it. I have yet to see any evidence that the U.S. was ever on the verge of revolution either before or after the rise of FDR. In 1932, for example, the Communists and the Socialists (primary indicators of radical or revolutionary sentiment on the left) scored between them a measly 2.5 percent of the vote. They did not elect a single member to Congress.
In 1932, FDR campaigned on a platform that differed little from that Al Smith in 1928 or, for that matter, his opponent Herbert Hoover. While he vaguely promised an undefined New Deal, he just as often attacked Hoover as a spendthrift. Politicians who promised retrenchment and low taxes, such as Governor Harry G. Leslie of Indiana, were often just as popular at the polls as those who promised more government.
To be sure, voters rallied to FDR's New Deal in 1933 but, in my view, this was primarily because they wanted action, not because of an ideological conversion. Given the poor state of the economy, it is probable that they would have climbed on board had FDR announced a program of spending and tax cuts instead. My sense is that the voters wanted change in 1933, not necessarily more government.
While quasi-fascists (actually populists) like Huey Long and Father Coughlin made waves, this was mostly in 1934 and 1935. If FDR"saved" the United States from the likes of them, why did they have their best years after his New Deal was implemented. Long's high point, for example, was 1935, when the NRA was already on its last legs.
I have a challenge for those who argue that FDR"saved capitalism." They need to start by answering two questions. When precisely did he"save capitalsm" and who did he save it from?