Libertarians are usually an afterthought in American presidential politics, but they could make a dent in the two major parties’ support this year.

The party, which is likely to be the only one to appear on the ballot in all fifty states after the Democrats and Republicans, will try to lure young, liberal Bernie Sanders supporters away from Hillary Clinton, the presumptive Democratic nominee, while simultaneously being a refuge for small-government conservatives who are appalled by Donald Trump’s authoritarian streak.

It’s a careful balancing act, complicated by the Libertarians’ tendency to shoot themselves in the foot.

Serious effort

The wackiness Americans tend to associate with Libertarians was on display at their national convention in Florida this weekend, where crowds booed suggestions that government has a role in issuing drivers’ licenses. The fact that the conclave shared a convention complex with comic book fans didn’t help optics either.

But the convention ended up nominating former Massachusetts governor William Weld, once a Republican, as its vice presidential candidate, signaling a seriousness to contest the election in November.

Gary Johnson, the former New Mexico governor, was nominated for the presidency a second time. He got less than 1 percent of the vote in 2012.

Polls mean little this far out from the election, but for what it’s worth: three recent surveys have given Johnson around 10 percent support nationally.

He needs at least 15 percent to qualify for the televised presidential debates, which, for a third-party candidate, are critical to reaching a national audience.

Calculation

The trouble for all third parties is that voters fear inadvertently helping the candidate they like least.

Polls consistently show pluralities or even majorities of Americans agree with Libertarians on shrinking government, lowering taxes, legalizing marijuana and scaling back America’s presence around the world.

But a Bernie Sanders supporter who isn’t crazy about Clinton is unlikely to want to risk a Donald Trump presidency.

The Libertarians’ hope is that some Republicans will make a different calculation. A minority refuses to fall in line behind Trump and can probably live with the relatively centrist, internationalist Clinton if all else fails. A Republican-lite Libertarian ticket could just give them the excuse they need not to vote for their own party this year.