Why Pennsylvania Could Decide The 2016 Election

05.18.16 | Bob Price

When most people think of battleground America, they think of Florida and Ohio, two of only three states (along with Nevada) that have voted for the winner of every presidential election since 1996. They tend not to think of Pennsylvania as a classic “swing state” — it has voted for the Democrat in every election since 1992, and it didn’t even crack the top 10 in 2012 campaign ad spending.

But in 2016, Pennsylvania could be the keystone of the Electoral College and the ultimate arbiter of whether Donald Trump or Hillary Clinton resides at 1600 Pennsylvania Avenue.

The term “swing state” can be a bit fuzzy. For example, we often call Michigan and North Carolina swing states. But if a Republican is winning Michigan, they’ve likely already won the election; the same is true for a Democrat winning North Carolina. In other words, after all the sturm und drang, these states tend to be icing on the winner’s cake. But a few years ago, Nate Silver articulated a much more valuable concept: the “tipping point state.” This is defined as the state that provides the presidential winner his or her 270th electoral vote when all states are rank-ordered by his or her highest to lowest margin of victory. Over time, this state has shifted: In 2000, it was Florida. In 2004, it was Ohio. In 2008, it was Colorado.

In 2012, President Obama’s three closest wins were Florida (by 0.9 percentage points), Ohio (by 3.0 points) and Virginia (by 3.9 points). But even if Mitt Romney had flipped all three states to his column, he would have still fallen four Electoral College votes short of the White House. The “tipping point state” was a virtual tie between Colorado and Pennsylvania, which both voted for Obama by about 5.4 percentage points.

In 2016, Florida and Ohio will likely remain necessary for Trump to obtain 270 electoral votes. Predictions that 2016’s Clinton vs. Trump showdown could “scramble” the traditional red/blue map are probably overblown; political scientists1 John Sides and Andrew Gelman have found that over time, year-to-year swings between the states are getting smaller. That said, the ordering of the battleground states — from most Republican leaning to most Democratic leaning — is unlikely to stay the same, especially because 2016 is an open election.

I’d argue Pennsylvania has leapfrogged Colorado and Virginia as the next most winnable state for Republicans. In fact, it may be on pace to claim sole “tipping point” status.

I arrived at this conclusion by calculating each state’s “six-cycle trend” — a measure of how much more Democratic or Republican-leaning each state has trended relative to the nation as a whole since 1992. To do this, I compared Obama’s 2012 two-party vote share in each state to the Democrat’s share in each of the five prior elections, then took the average of those differences, controlling for national swings and the number of four-year intervals.2

For example, California voted 5.1 percentage points more Democratic than the nation overall in 1992, but 9.9 points more Democratic than the nation in 2012, for a trend of 0.96 percentage points towards Democrats every four years. I recalculated this differential versus 2012 for every year between 1996 and 2008, and took the average. California’s resulting “six-cycle trend” was 1.46 percentage points towards Democrats. By contrast, West Virginia’s was 4.66 percentage points towards Republicans.