SALENA ZITO: Trump could lose Pennsylvania in 2020 if the Dems hone their message.

Trump won Pennsylvania by just 44,000 votes in 2016, the first Republican to take the state since 1988. That margin is so thin, the state could easily be won by a Democrat in 2020.

But if the Democrats want a victory, they must hone their message. Because here’s the other takeaway from last week’s statewide elections: the Western suburbs around Pittsburgh are deepening their allegiance to the GOP.

As Mike Mikus, a Democratic strategist in Western Pennsylvania, puts it: “Philadelphia got bluer and Western Pennsylvania got redder.”

In short, not all suburban voters are alike.

“Go too far left on policy positions like banning fracking or Medicare for All or taking people’s guns away anywhere outside of the counties of Philadelphia, and they might repeat the same mistakes of 2016,” said G. Terry Madonna, political-science professor at Franklin and Marshall College.

Plus, voters in Pennsylvania are fickle, which is one reason why it — along with Wisconsin — remains the country’s most important swing state. Bucks County, just north of Philadelphia, proves just how easily voters can switch.

Zito was among the first (or maybe even the first) national reporters to see and understand the Trump phenomenon in 2015, so ignore her at your own peril. That said, if the Dems can lose PA’s swing votes with promises of “banning fracking or Medicare for All or taking people’s guns away anywhere outside of the counties of Philadelphia,” then maybe they’ve already lost.