If you want to assign blame for the botched invasion of Iraq, which helped give rise to ISIS, don't put it all on George W. Bush, Dick Cheney and compliant members of Congress who were swept along, like Hillary Clinton.

Save a share of it for Ralph Nader. If he weren't in the race, Al Gore would have won.

In this Sept. 3, 2016 file photo, Libertarian presidential candidate Gary Johnson speaks during a campaign rally in Des Moines, Iowa. (AP Photo/Scott Morgan)

Nowhere is this more obvious than in Florida, where Nader won roughly 100,000 votes. If just 1 percent had voted for Gore instead, he could have overcome Bush's margin of 537 votes and won the presidency. That is the hard math of politics. It's a zero-sum game.

Let's hope that America learned that lesson. Because a fresh poll from the New York Times and CBS News shows that we are at grave risk of repeating the mistake.

The poll has Clinton clinging to a small lead over Donald Trump in a head-to-head match. But the lead vanishes when minor party candidates are thrown into the mix.

In a four-way race, Gary Johnson, the libertarian, stands at 8 percent, while Jill Stein, of the Green Party, draws 4 percent. Clinton and Trump are locked in a tie at 42 percent.

Johnson and Stein are running to make a point, and each has some appeal. Johnson wants to call a cease-fire in the ruinous drug war, and to legalize marijuana, no doubt a key to his appeal among young voters. Stein would use a muscular government to create jobs and raise wages, as well as to protect the environment.

Look deeper, though, and the appeal fades. Johnson would eliminate corporate taxes, shrink the government by nearly half, eliminate the Department of Education, and pull back federal efforts to fight climate change. Stein's views are so far left that none would have a prayer of winning support in Congress.

For many people, voting is an expression of identity. If they don't want to be a Trump or Clinton person, they can escape the trap by embracing Stein or Johnson. They can keep their hands clean. You can see the bumper stickers now: "Don't blame me. I voted for Stein."

But remember the stakes. Donald Trump is genuine threat to America and has to be stopped, even at the risk of getting your hands dirty.

This man is dangerous. He says he might not honor the NATO treaty if Russia attacks Europe, which no doubt tempts his buddy Vladimir Putin. He says we should steal Iraq's oil and bring back torture with more vicious techniques, moves that will drive away allies and give ISIS a potent recruiting tool. He says he'll impose a 45 percent tariff on Chinese imports, which would prompt a ruinous trade war. His would use the machinery of government to impose a religious test on Muslims.

He lies constantly, and it's all been documented. He has a long history of racist behavior and comments, he slanders Latinos and immigrants generally, and his bigotry towards Muslims is beyond dispute. No, thousands of Muslims in Jersey City did not celebrate the 9/11 attacks. It's another vicious lie.

He would offer deep tax cuts to the rich, people like himself. He would role back all efforts to combat climate change, which he calls a hoax invented by China. And his business record is full of slimy bankruptcies that left small business owners with unpaid bills, and students at Trump University making credible claims that they were ripped off.

Given these stakes, the moment demands a vote for Clinton. A vote for Stein or Johnson would risk repeating the mistake Nader voters made in 2000, but with much higher stakes.

The point of this exercise is not to feel good. We are picking a president. It's time to think strategically. If you get your hands dirty, show them to your neighbors with pride.

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Tom Moran may be reached at tmoran@starledger.com or call (973) 836-4909. Follow him on Twitter @tomamoran. Find NJ.com Opinion on Facebook.