Populism is definitely a part of democracy, but it is a criticism from "responsible" politicians for "irresponsible" ones.
Obviously this is all politics so you needn't worry about the specifics of what actually is populist.
But, imagine two "responsible" politicians.
One who believes in lowering taxes as a worthwhile thing, and acknowledges cuts to services as a negative impact that is outweighed by the good.
The other believes in higher public spending, with the negative being higher taxes, outweighed by the better services.
Both would be angered by a third candidate that came along promising both lower taxes and higher public spending - just the "popular" parts of their respective manifestos.
So by that logic both democrats and republicans are populist parties, because neither is willing to propose the hefty middle class tax increases, or entitlement cuts, that are mathematically necessary to balance the budget (much less to fund additional programs). Do I have that correct?
Potentially - it's not like a strictly defined term. With mainstream political parties you'd more often think about specific policy areas than the whole business.
Obviously this is all politics so you needn't worry about the specifics of what actually is populist.
But, imagine two "responsible" politicians.
One who believes in lowering taxes as a worthwhile thing, and acknowledges cuts to services as a negative impact that is outweighed by the good.
The other believes in higher public spending, with the negative being higher taxes, outweighed by the better services.
Both would be angered by a third candidate that came along promising both lower taxes and higher public spending - just the "popular" parts of their respective manifestos.