Liberals are beset by their own internal divisions.
The American left believes that the center-left is far too conservative, and they often say that there's no difference between the Democrats and Republicans. It's widely said that the party insiders control the process to exclude them.
Democrats occasionally fall in love with a charismatic leader like Obama or Bill Clinton, but if they don't they have a hard time winning a national election.
By contrast, Republicans nearly always fall in line. One might naively expect that moderates would have trouble getting behind a multiply-convicted candidate beset with hundreds of millions of dollars in fines, but he's likely to be the next nominee, and there's no sign that significant numbers will be deterred.
Nationalism has the enormous advantage that people pull together against their enemy. I know of nothing that liberals can do to counteract that pull. They don't have another ultra-charismatic type waiting in the wings. No argumentation is ever going to pull away people devoted to nationalism.
The best liberals can hope for is to at least agree that the nationalist party is going to cause them tremendous harm. They failed badly to do that in 2016, and I don't really think they've learned any lessons.
