...Populism is politics which opposes wealth and power in the name of the common folk. It takes both left wing and right wing forms and sometimes degenerates into bigotry and attacks on minorities. ...Populist appeals can be made by spokesmen for special interests who have no intention of fulfilling their democratic promises, but who are just opportunistically faking populism as part of an attack on some enemy. (As I never get tired of saying: Republican populism is fake, but Democratic elitism is real).
...Since the Fifties the Democratic Party, whose populist wing was critically important during the New Deal, has avoided and repressed populism. Individual populists such as Paul Wellstone have occasionally been elected, often in defiance of the party machine, but they have never had much influence in the party. The Democratic strategy has been cooperation with big business, and their slogan has been "a rising tide lifts all boats" -- "win-win" solutions where everyone wins and nobody loses. This worked pretty well until about 1970, when business started to pull away from the deal, and since that time it's been mostly downhill for the Democrats, for labor, and for the average American.
[Look no further than this article for confirmation; Barney Frank, Defender of Un-Regulated Derivatives!!!]
The linked article is lengthy, but those excerpts should get you going.
There's no question that "populism" is a ping-pong ball. The Democrats use it when out of office, and the Republicans return the favor, by no coincidence when THEY are out of office.