Libertarian presidential candidate Gary Johnson is zeroing in on a key challenge for his longshot campaign: Boosting his support in the opinion polls so he can qualify for the general-election debates.

One recent poll gives him 10 percent support against Democratic candidate Hillary Clinton and Republican candidate Donald Trump. "As you have probably noticed," Johnson said in an email to supporters and reporters, "as more polls include my name and show us in double digits, a funny thing is happening. Not only is the news media taking TO Governor [William] Weld [the former Republican governor of Massachusetts and Johnson's vice-presidential running mate] and me more, they are now talking ABOUT us more. And, of course, that is precisely what we need."

Johnson got 10 percent in the most recent NBC News/Wall Street Journal Poll, and Green Party candidate Jill Stein got 6 percent. Clinton led with 39 percent and Trump had 38 in a four-way race.

"But this increased recognition is nothing compared to what will happen when I begin to consistently gain 15 percent in those polls – just a few points higher than where we are today," Johnson added. "At 15 percent, the media, and voters, will take note of the fact that 15 percent puts us in the presidential and vice-presidential debates this fall. ... Being in the debates is a game-changer." Johnson is the former Republican governor of New Mexico and a businessman who was the Libertarian candidate for president in 2012. He bills himself as socially liberal and fiscally conservative.