You misunderstand. Harris picking a pro-Israeli IDF veteran VP might cause some folks in Dearborn or Hamtramck to stay home. They're not voting for Trump. Why would they? He's even more pro-Israel than Shapiro is.

Some have claimed they're going to - that there's no difference between Biden and Trump on Israel ("Genocide Joe" and all that), so it doesn't matter which one is President next term. So switching to Trump costs them nothing, but sends a powerful message. They think. I personally think they're foolish for thinking that, but that's what they think.

But staying home (or voting for West or Stein or Kennedy) is still damaging. Biden backing the border bill would have lost him the immigrant advocate vote in the same way - even if they didn't switch to Trump, they also might have stayed home or voted third party. So if you lose the advocate vote simply by passing the bill, it makes zero sense to not try to pick up the centrist votes by exercising the powers and getting the numbers down.