Gary Johnson keeps pitching his presidential campaign to Bernie Sanders' disappointed supporters. Read any profile of the Libertarian nominee, and chances are you'll get to a part where he points out that the ISideWith site says Sanders is the rival candidate he agrees with the most.

It's not hard to see why he's doing this. While there are big differences between Johnson's and Sanders' economic platforms, their views have more overlap when it comes to social and foreign policy. Presumably there are some Bernie backers out there who care more about the latter issues, and Johnson would like to reach them. And indeed, according to a recent Bloomberg poll, "barely half of those who favored Sanders—55 percent—plan to vote for Clinton. Instead, 22 percent say they'll vote for Trump, while 18 percent favor Libertarian Gary Johnson." Eighteen percent is a pretty big slice of the pie, especially for a third-party candidate.

So yes, it makes sense for Johnson to pursue those voters. Two big caveats apply, though.

First: No matter what the people in the survey are saying now, Hillary Clinton's 55 percent share is almost certain to grow. The supporters of a defeated candidate are far more likely to say things like this at the end of the primary season than they are in November. A number of the people telling Bloomberg that they'll back Johnson may just want to signal that they don't like Clinton but cannot bring themselves to declare that Donald Trump's their man. That doesn't mean they'll actually pull the Libertarian lever in November.

That's especially true in light of the other caveat: The poll didn't mention the likely Green nominee, Jill Stein. Yet when it comes to pursuing Sanders voters, Stein has an advantage over Johnson—she agrees with more of Sanders' platform. When a Bloomberg reporter interviewed someone who showed up in the survey as a Sandersite for Johnson, he revealed that he actually plans to vote Green:

Eric Brooks, 52, a community organizer in San Francisco, won't [vote for Clinton]. "I will absolutely never vote for Clinton," says Brooks, a Sanders supporter who participated in the Bloomberg poll. Although Brooks indicated in the poll that he'll support Johnson, that is not his intention. "I'd be okay voting for Johnson as a protest vote," says Brooks. "But as a Green Party member, I'm going to vote for [Green Party candidate] Jill Stein. If you care about the climate, like I do, it makes a lot of sense strategically to vote for Stein, because she could get five percent, which has implications for the Green Party getting federal funding."

That said, Johnson will probably appear on more ballots than Stein. The Libertarian ticket may not have much hope of carrying the San Francisco community organizer vote, but perhaps it'll do better with the frustrated leftists of Tulsa.

In the meantime, Johnson's immediate target isn't the election in November. It's the presidential debates, which start in September. At that point, Johnson will need to be getting 15 percent in five national polls to be onstage with the Democratic and Republican nominees. If he makes it, I doubt he'll mind if he got an assist from some people who ultimately will vote for Clinton or Stein instead.

Bonus reading: "Sanders Voters for Trump."