Please don't use the word "liberal" as interchangeable with "left".

Democrats are liberals, yes, as in proponents of liberalism, as in proponents of the natural rights of the individual crucially including the right to own private property. Liberalism is in other words the political philosophy of capitalism.

Left, on the other hand, basically means that relative to another party or ideology, a given party or ideology favors greater equality or less hierarchy. Democrats are today generally left of Republicans, albeit not by much. Democrats, however, are not leftist — because leftism generally points specifically to Marxists, anarchists, and other people who specifically want to abolish private property.

In other words, if you're only thinking of Democrats and Republicans, then Democrats are "the left"; but if you're including all the Marxists and anarchists around, then Democrats are suddenly on the right. The equation of "liberal" with "left" in the USA then serves to confuse people and limit their imagination and understanding: it is best to draw the line between left and right at the point of preserving or abolishing private property, because when one party wants to completely change the whole mode of production of society, and another wants to keep the mode of production as-is, then their use of slogans about the plights of minorities are a purely superficial point of comparison.