Liberalism (the modern, post New Deal sort, not the classical liberalism of J. S. Mill so commonly butchered by right-libertarians) is a dying ideology that has only ever been powerful when it served as a capitalist safety valve, releasing the social pressures built up by a powerful socialist and communist movement. When it is responding to the Left it has some measure of vitality and intellectual substance; I'm a big fan of J.K. Galbraith's The Age of Uncertainty and was quite astounded by how subtle and even radical parts of it were.
However, ever since the collapse of the American socialist movement in the 60s and 70s and in particular since the collapse of the Soviet Union a generation ago (which provided no real strong moral or economic challenge for decades at that point anyway), liberals have been primarily responding to the right wing, to their detriment. It is one thing to provide a less risky compromise to the politics of revolution. It is quite another to merely dedicate yourself to crushing the working class a little more slowly or to smile while doing so.
This has led a to a hollowing out of the Democratic policy-creating apparatus, a breakdown in the formation of new ideas, the abandonment of whole swathes of the population with a smug "where else are you gonna go?" attitude, and in general a total collapse in intellectual and moral integrity. This much is clear to any informed observer of politics and the electoral results don't lie.
We can even follow a sort of history of groups responding to each other: for a few decades, when liberalism was ascendant after responding successfully (with more than a little help from violent State repression) to the Left, a whole tradition of "intellectual" conservatives arose to respond to it in turn, attempting to move past the old open oligarchy and praise of unregulated markets and cold indifference to the poor.
The first major sign of liberalism's decline might have been the quick die-out of these intellectual conservatives after Reagan and their replacement with vulgar hacks who didn't even deign to hide their open bigotry or Gekko-like greed - why bother when liberalism was quickly losing the ability to challenge those things? The class of intellectual conservatives today includes David Brooks (himself closer and closer to a caricature) and a tiny handful of others; they serve primarily as a way for liberals to feel like they are reading and respecting different opinions, which is why they inhabit places like The New York Times instead of writing for newspapers that conservatives actually read. And now liberalism is following in the footsteps of the vanishing Brooksian tribe.
Until and if (for there is no guarantee) liberalism regains a sense of moral justice and a desire to engage with its socialist critics, you can expect the following tactics to be used almost exclusively: substance-free mocking, smearing, doxxing and attempts to get people fired or ostracized from their friends and family, and attempts to silence and no-platform critics. They don't have ideas and they don't have arguments, so this is what they are reduced to. It's a very poor hand to be playing and I suspect many of them know it, but they don't have a choice in the matter.
So one thing they keep pushing are idiotic comparisons between socialists and neo-Nazis - and a big part of this is the forced attempt to make "alt-left" a meme. If we are the alt-left then we're just as bad as the alt-right, don't you know? Only those in the middle are smart and reasonable and everyone else is dumb and evil.
Fight back against this nonsense. Reframe arguments to be about justice & freedom. Point out the awful smear and silencing tactics in lieu of of actual argument and debate - start pushing actual ideas. Liberals have little or no responses to any of these things and they will get quickly frustrated; no matter, you're arguing to audiences, not people tied to a quickly dying ideology. We can and will make inroads with those who are wavering in their beliefs.