Is it possible for the slightly extreme left and the slightly extreme right to come together in America?

So the United States has two viable political parties. Republicans and Democrats. Those parties are constantly torn between appealing to their “base” and appealing to centrist independents. There are plenty of people, both on the right and the left who feel like neither party is doing what they want them too, but vote for what they see as the lesser of two evils. Some of those people are real extremists, but some are what I consider less extreme. Your garden variety small “l” libertarians and (no need for small letters because this party doesn’t exist in the U.S.) social democrats. That’s my word, maybe we’re greens, or even socialists, but I think social democrat fits best. Could the libertarians and the social democrats ever find common ground in a candidate or a party platform, and elect someone we could all believe in, who would actually appeal to independents a lot more than the so called centrists? What policies could we agree on? What are the irreconcilable differences?