‘I’m doing what I’ve never done,” said a lifelong Democrat and friend of mine, “and pulling a Republican ballot” in next month’s Illinois primary.

Voters and we media types jabber about this kind of crossover every primary election cycle, especially when the stakes are higher on one side of the ballot than the other. It sounds rational, plausible, even logical.

But it almost never happens.

For the most part, each of us sticks to the political camp with which we’ve traditionally identified when we go to pull a primary ballot.

Could this election be an exception?

Consider the landscape of the March 18 primary.

On the Democratic side is incumbent Gov. Pat Quinn vs. largely unknown and vastly unfunded challenger Tio Hardiman. Low job-approval ratings or not, Quinn is regarded as a shoo-in.

On the Republican side of the ballot, the governor’s race is where the action is. There are four credible contenders. Three who have run statewide before — Bill Brady, Kirk Dillard and Dan Rutherford — plus one previously unknown billionaire, Bruce Rauner, who has saturated the airwaves and, according to recent polls, is in the lead. Though a fifth contender, “undecided,” is in the hunt.

The unions, apoplectic over Rauner’s antipathy toward organized labor, have vowed to go to war in what they view as a fight for their very survival in Illinois. But if their heavily Democratic membership crosses over, and if they view Rauner as the villain, who then is their alternative?

That’s the problem.

As united as some major unions might be in their anti-Rauner sentiment, there is no widely organized effort to zero in on an alternative.

As I write this, state Sen. Kirk Dillard of Hindsdale, who very nearly won the Republican primary in 2010, has just gotten the endorsement of the 133,000-member Illinois Education Association. And IEA President, Cinda Klickna declared Friday, “This is such a crucial election. . . . We are going to be taking a Republican ballot.”

The IEA, composed of mostly suburban educators, has weighed in on Republican primaries in the past. But most other unions have not.

Why not?

As one high-ranking union official told me on Friday, “The notion that union members — or other voters — will vote against the party with which they are affiliated is an urban myth. It doesn’t happen.”

David Yepsen, head of the Paul Simon Public Policy Institute, agrees. A legendary former political reporter himself, Yepsen puts it this way: “It could happen. But not likely. Every campaign I’ve ever been around, you’ll hear those anecdotal stories (of voters crossing over) but you don’t see it.”

Meanwhile, the variables for the Illinois primary are, simply put, huge.

State Treasurer Dan Rutherford’s campaign, at the moment, is imploding over unproven but explosive allegations of sexual harassment. If Rutherford’s voters defect, to whom?

“Undecided,” says Yepsen, is a real possibility. “When something like this happens, people don’t just jump from one candidate to another. They think it over for a while.”

Four weeks.

And counting.

Email: cmarin@suntimes.com

Twitter: @CarolMarin