Donald Trump. AP Obviously, the last week has been a disaster for Donald Trump and the Republican party. But the situation is even worse for Republicans than it looks at first glance.

Downballot Republicans face a grim choice: Repudiate Trump and annoy the great many Republican base voters who are big fans of his, or stick with Trump and alienate swing voters (while also flushing what dignity they have left down the toilet.)

An "undervote" is the term for when a voter casts a ballot but does not vote in a particular race. As some Republicans stick by Trump and others reject him, the party is at grave risk of triggering what I'll call the triple undervote.

Some pro-Trump voters will show up to vote for him but withhold their votes in downballot races, out of anger at a Republican party they see as sabotaging the nominee primary voters chose.

Some anti-Trump Republicans will show up to vote, but not vote for Trump at the top of the ticket.

Some Republican-leaning voters who are disgusted by the whole situation won't show up to vote at all.

When you combine those three effects, the result is that Democrats can win up and down the ballot even if most of the voters in a given state or district lean Republican.

It's a total nightmare for Republicans. And it's a reason rejecting Trump en masse may not help the party protect its House and Senate majorities.