As Jeb Bush exits the presidential race and Donald Trump marches on as the Republican frontrunner, it’s worth considering a counterfactual: Without Bush, would Trump’s candidacy have even gotten off the ground?

There’s evidence to suggest Bush’s mere existence as a presidential candidate was enough to prime the Trump engine. As Obi-wan Kenobi might have put it, Trump and Bush formed a symbiont circle—what happened to one affected the other.