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Without Tim Kaine, Hillary Clinton might have lost Virginia as well

Sen. Tim Kaine, right, and former president Bill Clinton applaud as former secretary of state Hillary Clinton delivers her concession speech on Nov. 9 in the presidential race. (Jewel Samad/AFP/Getty Images)

In last week’s presidential election, Hillary Clinton lost nearly all the swing states. However, Clinton managed to cling to Virginia — the home state of her running mate, Sen. Tim Kaine (D).

Did Kaine’s presence on the ticket help save Virginia for the Democrats? We believe it did.

Some political science research argues that vice-presidential candidates do not significantly impact the vote — even in their home state. In contrast, our research shows that VP candidates add an average of nearly 3 percentage points to their ticket’s vote in their home states.

Our research relies on a new approach to measure the vice-presidential home state advantage, known as “synthetic controls.” For each running mate, we use a combination of similar states to construct a “synthetic” version of their home state, which mirrors the electoral results of the home state over a series of past elections.

For example, to estimate how much Vice President-elect Mike Pence helped the Republican ticket in Indiana, we constructed a “synthetic Indiana” that combines Nebraska, Montana, Pennsylvania, Hawaii, Utah and Alabama. None of these states, on their own, perfectly match Indiana in the last several elections. But once combined, the Republican vote share in “synthetic Indiana” looks quite similar to that of Indiana from 1984 to 2012.

The difference between Indiana and “synthetic Indiana” is that “synthetic Indiana” does not have a home state running mate on the ticket in 2016. The gap that emerges between the two versions of Indiana, in 2016, is our estimate of Pence’s home-state advantage: 2.53 points.

Given the GOP’s strength there, Pence’s presence on the ticket did not flip the state. Indeed, as we noted after Pence’s selection, Indiana is a reliably Republican state. Trump would have received nearly 58 percent of the vote there even without Pence’s support.

Kaine’s influence in Virginia is a different story. Our estimate is that Kaine added 2.81 points to Clinton’s vote share. Given that she received only 52.78 percent of the two-party vote in Virginia, this means she could have lost Virginia  if not for Kaine — although it would have been quite a nail-biter.

Nevertheless, Kaine’s potential impact on the outcome shows the value in selecting a running mate from a major swing state. If Clinton had performed slightly better in other swing states, while still needing Virginia to hit 270 electoral votes, Kaine could have been a true game-changer. Future presidential nominees should use this knowledge to their advantage.

Boris Heersink is a PhD candidate in the Woodrow Wilson Department of Politics at the University of Virginia. Brenton D. Peterson is a PhD candidate in the Woodrow Wilson Department of Politics at the University of Virginia and a research affiliate at Strathmore University.