I’ve been going over what was said at Wednesday’s Republican debate, and I’m terrified. You should be, too. After all, given the vagaries of elections, there’s a pretty good chance that one of these people will end up in the White House.

Why is that scary? I would argue that all of the G.O.P. candidates are calling for policies that would be deeply destructive at home, abroad, or both. But even if you like the broad thrust of modern Republican policies, it should worry you that the men and woman on that stage are clearly living in a world of fantasies and fictions. And some seem willing to advance their ambitions with outright lies.

Let’s start at the shallow end, with the fantasy economics of the establishment candidates.

You’re probably tired of hearing this, but modern G.O.P. economic discourse is completely dominated by an economic doctrine — the sovereign importance of low taxes on the rich — that has failed completely and utterly in practice over the past generation.

Think about it. Bill Clinton’s tax hike was followed by a huge economic boom, the George W. Bush tax cuts by a weak recovery that ended in financial collapse. The tax increase of 2013 and the coming of Obamacare in 2014 were associated with the best job growth since the 1990s. Jerry Brown’s tax-raising, environmentally conscious California is growing fast; Sam Brownback’s tax- and spending-slashing Kansas isn’t.