Democrats used to take the bribes from unions. It was crooked but it kept something of a balance.
Then Reagan convinced his "opposition party" in the 80s to take the same oligarch cash Republicans took instead, as it comes with more zeroes than unions could ever hope to provide. Thus the Neoliberal-Republican alliance was struck on economic policy.
We have no pro-union party in America functionally. The Neoliberal party still pays lip service to unions, when they aren't legislating against their interests with Republicans.
But oooh, you watch them fight over social issues (that are largely exacerbated by our rigged economic system), and you'd think Neoliberals and Republicans are at odds or something!