I don't know what "extremely liberal" would be. Liberalism isn't really a very extreme sort of thing. A socialist, say, would be to the left of liberal and might view a liberal as being pretty mainstream, by definition (though on the left side of the mainstream). It's only since the Moral Majority that "liberal" got recast as being "extreme", and I'm not sure a lot of people know what they mean when they say that.
See, hard to keep the politics out of a thread like this one.
By the way, around the same time (1980), the last liberal Republican that I know of to run for President, John Anderson, fizzled out, but they existed. so that complicates things. Where would he fall on the poll? Or Libertarians?