As the 2016 Election season was nearing completion, Paul Krugman wrote the following editorial ('Trump's Fellow Travellers', in The New York Times ,...

As the 2016 Election season was nearing completion, Paul Krugman wrote the following editorial ('Trump's Fellow Travellers', in The New York Times, 3 Oct. 2016, A23):

While almost all Republican officeholders have endorsed Mr. Trump, the same isn't true of what we might call the G.O.P. intelligentsia—actual or at least self-proclaimed policy experts, opinion writers, and so on. For the most part, the members of this group haven't spoken up in support of this year's Republican nominee. For example, not a single former member of of the Council of Economic Advisers has endorsed Mr. Trump. If you look at who has endorsed Mr. Trump—say, the signatories of the statement of support from "Scholars and Writers for America"—it's actually a fairly pathetic group.

But if you think electing Mr. Trump would be a disaster, shouldn't you be urging your fellow Americans to vote for his opponent, even if you don't like her? After all, not voting for Mrs. Clinton—whether you don't vote at all, or make a purely symbolic vote for a third-party candidate—is, in effect, giving half a vote to Mr. Trump.

Reconstruct Krugman's main argument in premise-conclusion form.