WORRIED: Democrats target Libertarian ticket.

The Libertarian ticket of Johnson and Bill Weld is running surprisingly strong among young voters — a cog in the Obama coalition that Democrats need to turn out for Clinton if she’s to pull away from Trump.

Whether Clinton reaches those voters could determine the outcome of critical battleground states like Colorado, Nevada and Pennsylvania.

Democrats still vividly remember the 2000 election and blame Ralph Nader for costing Al Gore the presidency in the closest election in history. They’re worried history could repeat itself in 2016, as third-party candidates are attracting more interest than they have in decades.

The Clinton campaign and its liberal allies are increasingly taking the threat from Johnson and Stein seriously, making direct appeals to young voters and punching down at the third-party candidates they view as potential spoilers.

“Young voters are suggesting that they’re uncomfortable with Clinton and are using Johnson and Stein as protest votes,” said Douglas Schoen, a former official in the Bill Clinton administration. “The campaign must make the case that unless young people vote for Clinton, they’re effectively voting for Trump.”

I’m not sure how much difference young voters see between the two near-septuagenarian major party candidates.

But mostly Democrats should be asking themselves why the Libertarian Party’s least-likely nominee ever is doing so well with a traditional Democratic constituency.