In short: the Johnson-Weld campaign has emphasized all along that it draws from left and right alike. They’re right. Indeed, they’re so right that it does not seem like the Johnson-Weld campaign– even at high levels of support, like the 13% they had in Quinnipac, or the 10%+ they had in 42 states in WaPo/Survey Monkey– will tilt the presidential election one way or the other. (Remember, even at those levels of support there doesn’t seem to be even a single state that they’re flipping.) But the balance tilts a little bit toward “they’re taking votes from Trump,” for an overall result that’s something like a 2% net benefit to Clinton. If the race stays as close as it now looks– which I don’t expect– that could matter.

If I can do this math, so can the Johnson-Weld campaign– and so can the Clinton campaign. Stein is a real problem for Clinton. But the Johnson-Weld ticket is an opportunity. If I’m right that Trump’s support among Republicans remains fragile– if traditional Republicans are uneasy keeping company with neo-Nazis and the Klan, or worried on national security grounds about Trump’s ignorance and instability, or constitutionalist enough to dislike his embrace of authoritarians abroad and of strongman executive demagoguery at home– then increasing visibility for Johnson-Weld could well have a very asymmetrical effect.

Clinton supporters when confronted with this are prone to say things like “those Republicans should vote for Clinton.” And we’re starting to see the signs of some Clinton surrogates gearing up for a scorched-earth campaign against Johnson on those grounds. But those disgruntled Republicans won’t vote for her– for reasons having to do with decades of annoyance with the Clintons, or for reasons of the basic tribalism of partisan identity. Taking half a step away to vote for former Republicans is a lot psychologically easier for many Republicans than taking a full step away to vote for a Clinton. And so, if anything, I would expect the net benefit Johnson-Weld provide to Clinton to grow a bit if his support grows further. In any case, on current evidence, the Libertarian ticket is having a largely neutral but slightly pro-Clinton effect on the race as a whole, and this fact is being widely misreported because people are improperly lumping together the effects of Johnson and Stein, then attributing that effect to the Libertarians along in a classic fallacy of division.