Roosevelt succeeded, in part, because he had elected progressives & leftists, nationwide, at all office office levels, demanding action.
The economic depression that began in 1929 helped to sweep the Democrats and Franklin Delano Roosevelt into office in 1932. With his New Deal the Democrats were identified as the party of reform.
Roosevelt was reelected in 1936 with the largest plurality in the nation's history, and in 1940 he became the first U.S. President to be elected to a third term. After leading the country for three years in World War II, he was reelected for a fourth term in 1944.
The economic downturn of 1937–38, and the bitter split between the AFL and CIO labor unions led to major Republican gains in Congress in 1938 effectively ending completion of many of the gains made by Progressives, Liberals and Leftists in the New Deal laws and programs.
New Deal From Wikipedia
The realignment crystallized into the New Deal Coalition that dominated most presidential elections into the 1960's, while the opposition Conservative Coalition largely controlled Congress from 1937 to 1963.
By 1936 the term "liberal" typically was used for supporters of the New Deal, and "conservative" for its opponents.
From 1934 to 1938, Roosevelt was assisted in his endeavors by a "pro-spender" majority in Congress (drawn from two-party, competitive, non-machine, Progressive, and Left party districts).
As noted by Alexander Hicks, "Roosevelt, backed by rare, non-Southern Democrat majorities—270 non-Southern Democrat representatives and 71 non-Southern Democrat senators—spelled Second New Deal reform." In the 1938 midterm elections, however, Roosevelt and his liberal supporters lost control of Congress to the bipartisan Conservative Coalition.
We need progressive and leftists to run nationwide. Find and office and run for it. Organize your district and get your votes out. Start the wave that is coming and move up to Congress with as it rises.
Note: The campaign to get people to run has almost nothing to do with whom the Democrats elect in 2016 but a lot to do with how America is governed starting in 2016 & 2018 & 2020.