Donald Trump has compounded his error in choosing J.D. Vance as his running mate by essentially handing off the campaign to the Republican senator, according to a new analysis. The former president tapped the 40-year-old Vance before President Joe Biden exited the race and endorsed his own vice president, Kamala Harris, and The New Republic’s Alex Shepard said the GOP candidate has been “the worst running mate in American political history.” “Vance was chosen under the assumption that they were headed toward a landslide victory and therefore it really wouldn’t matter, even by the standards of …