In election parlance, a spoiler is a candidate who exists on the ballot as an upset for the presumptive nominee's chance at being elected. In the Republican camp this year, the spoiler comes in the form of Gary Johnson. Johnson is a libertarian who is the perfect choice to destroy Trump's chances - he's just controversial enough to make the transition easy.
Gary Johnson will likely play a spoiler in the upcoming presidential election. However, it is unclear which party Johnson will hurt this year. Traditionally, Libertarian candidates have always drawn off of Republican support. This year's election is so out of the ordinary that it is hard to say who he will draw his support from. Many Democrats are angry with Hillary as their party's nominee, so Johnson might actually pull more votes away from her.
Gary Johnson will not place boiler in the upcoming election because he does not have enough support to siphon away a meaningful number of votes from Donald Trump. Unfortunately, Gary Johnson is the best candidate of all but will not be elected. Unfortunately even worse, Hillary Clinton will win. God help us all when that happens.
No, Gary Johnson will not be be a spoiler in the upcoming election. Third-party candidates represent their own parties and beliefs, and as such, they represent the beliefs and ideals of groups of Americans as well. Voting for a third-party candidate does not spoil an election. Instead, it is simply an expression of what a voter wants. People shouldn't assume that supporters of a particular third-party candidate would have otherwise supported either of the two major party candidates.