Remember how close the 2000 election turned out? In Florida, the deciding state, Bush beat Gore by just 537 votes. Some Democrats blamed the loss on ultra-liberal Green Party candidate Ralph Nader, who received 97,421 votes. If Nader weren’t in the race, they said, Gore would have won.

Well, it’s 2012, and the tables are turned. Now it’s the Republicans who are worried about a third-party spoiler: Libertarian Gary Johnson. At first glace, you’d think Johnson would siphon votes from Obama; as a Libertarian, Johnson supports marijuana legalization and opposes war. But Johnson’s also anti-spending and anti-government. That means he’ll pull votes from the Ron Paul supporters—people who, presumably, would otherwise pick Romney over Obama.

Here in Nevada, Public Policy Poling found that Johnson pulls 3 percentage points away from Romney. Given how close the race is—many polls show the candidates in a dead heat, when accounting for the margin of error—those three points could make a huge difference. Yes, the number will probably go down in the coming weeks, given that Johnson won’t be included in the debates, unlike, say, third-party candidate Ross Perot, who went on to grab 20 percent of the vote in 1992. But it doesn’t take much to spoil a neck-and-neck horse race.

Johnson’s candidacy puts Libertarians in a tough position. Do they vote for the candidate with whom they most agree (Johnson), knowing full well he doesn’t stand a chance of becoming president? Or do they vote strategically, for their second choice (Romney)? That question may sound technical and wonky, but its answer could determine the future of our nation.