Blame me and everyone else in political journalism for the following myth: The Democratic Party is heading for a crackup just as the Republicans cracked up with the election of Donald Trump. Or, alternatively: Left-wingers are threatening to marginalize Democratic moderates the same way right-wingers did to Republican moderates.

That’s wrong, but it has the ring of rightness to it, because it gives the impression of fairness on the part of political reporters hoping to seem impartial. But this kind of false and forced equivalence distorts reality more than represents it accurately. The fact is, the parties are two species, not one. To attribute one’s genes to the other is to misrepresent parties and American politics generally.

But didn’t Sen. Dianne Feinstein lose the California Democratic Party’s endorsement? Wouldn’t state Senate leader Kevin de León’s victory illustrate the left’s infiltration of the party the same way moderate Republicans were primaried out of existence after 2008?

Maybe. Feinstein is a poor example of that trend, if there is a trend (a big if). She’s a four-term incumbent from California sitting on a mountain of cash with sky-high favorability in the age of Donald Trump. True, Feinstein is moderate. She’s been around since before her party’s center of gravity drifted left. True, she’s the oldest member of the U.S. Senate. But given all of her built-in advantages — incumbency, money, leadership in the opposing party — it’s hard to imagine anyone, even De León, unseating her.

But what about Bernie Sanders? Isn’t the independent senator from Vermont leading an insurgency?

You could say that — if “insurgency” means making noise, not winning power. Sanders endorsed a number of candidates after 2016, but a fraction of them has won. That’s not to say he’s having no impact. He clearly inspired activists to deny Feinstein the endorsement. The real question, however, is how much impact. From where I’m sitting, a majority of Democrats, meaning people who would support Feinstein, painfully remember Hillary Clinton’s defeat. For every activist Sanders fires up, he is alienating two or three run-of-the-mill liberal Democrats.

But aren’t extremist minorities agents of change? In the Republican Party, yes. In the Democratic Party, not so much. The reason, again, is differing party genetics.

The GOP is largely homogenous — racially, religiously, geographically and economically. And it is a top-down organization. When leaders make the call, rank-and-file Republicans tend to listen. Conditions like this made what used to be called the Tea Party a major force. It started small but was united and well-funded, and there was no downside to attacking the GOP leadership. Eventually, the Tea Party’s views became the Republican Party’s.

Not so for the Democratic Party. It is heterogeneous, as diverse as the country as a whole. It is more or less an egalitarian, or flat, organization. It is generally liberal, meaning individuals consider leadership’s views but leadership’s views do not supersede individual views. Organizationally, all of the above means Republicans are like herding sheep and Democrats are like herding cats. For extremist minorities to change the Democratic Party, they can’t divide and conquer, as the Tea Party did. They must build winning coalitions from the inside. That is, necessity prohibits them from being too extreme.

Genetics also explain differing approaches to the party in power. If the Tea Party stood for anything, it was extreme opposition to Barack Obama, even if Obama offered policy the GOP had wanted (like Obamacare). True, the Democrats are united against Donald Trump, but they won’t cut off their noses, because they must make room for the policy preferences of voters alienated by the president. For this reason, the more plausible claim is that the Democratic Party might grow more centrist rather than more leftist as long as Trump is in the White House.

Even so, expect the myth of the Democratic Party’s crackup to endure. The idea of an intra-party civil war is just too delicious for political reporters to pass up.