Pennsylvania remains one of the most crucial states in this year’s presidential election.

According to FiveThirtyEight, PA ranks second (behind only Florida) in their rankings of possible tipping-point states this November.

Furthermore, the Trump campaign has asserted for months that they believe PA can be part of a Rust Belt strategy that will turn traditionally blue states and provide a path to the White House.

In response, Steven Yaccino and Sasha Issenberg of Bloomberg Politics examined the electorates of the Rust Belt’s three biggest electoral prizes: Ohio, Pennsylvania and Michigan.

They found PA will likely be the hardest state to move because of the gulf of potential Democratic and Republican voters.

“Trump certainly needs to change the arithmetic in Pennsylvania,” Yaccino and Issenberg write. “The state hasn’t voted for a Republican presidential candidate since the late 1980s, and the math is straightforward: Democrats simply have more potential voters. They can count on a base of nearly 1.69 million votes, and—thanks in part to overwhelming support from African-Americans in Philadelphia—another 1.37 million less-reliable voters who can be mobilized through get-out-the-vote work.”

They point out that Southwest PA is a fertile ground for Trump to pick up disaffected Democrats, but as we’ve noted, while the GOP is likely to make gains in the Appalachian West the tide is against them in the Acela East.

Yaccino and Issenberg found that Ohio and even Michigan are much more likely to flip to Trump. This would be particularly significant as Pennsylvania hasn’t voted more Democratic than Michigan in a presidential contest since 1992.

Ultimately, with so few “persuadable targets”, Republicans must find a way to appeal to the suburbs of Pittsburgh and Philadelphia without alienating one or the other. Given the changing dynamics of each of those regions, they have quite the task ahead of them.