This picture obtained on his Facebook page on June 14, 2017, shows James T. Hodgkinson, who was identified as the shooter at the Republican congressional baseball practice in Alexandria, Va. (Agence France-Presse via Getty Images)

James T. Hodgkinson, the man who shot up a congressional baseball practice this morning, was allegedly a strong Democratic partisan who was outraged over the election of Donald Trump.

The Belleville News-Democrat, the paper in Hodgkinson's home town of Belleville, Ill., interviewed a few of Hodgkinson's neighbors today. One of the neighbors offered up a quote that speaks volumes about political culture in the United States.

“I didn’t really talk to him too much,” said neighbor Aaron Meurer. “He was a Democrat, and I was a Republican, so we didn’t have too much to talk about.”

In one sentence, Meurer offers up a snapshot of American partisanship: For many Americans, their political affiliation is a central component of their identity. Meurer's statement suggests that he and Hodgkinson saw themselves as partisans first and neighbors second.

This isn't to pick on Meurer — this sort of worldview is widespread and becoming more common in the United States. Recent data from the Pew Research Center speaks to the phenomenon directly. More than 4 in 10 Democrats and Republicans told Pew it would be easier to get along with a new neighbor if they were members of the same political party.

Conversely, 27 percent of Democrats and 31 percent of Republicans said it would be harder to get along with a new neighbor of the opposite party. In both parties, people who were highly engaged with politics were more likely to hold this view.

This intraparty antipathy is rising rapidly. In 1994, according to Pew, 21 percent of Republicans, and 17 percent of Democrats, held rated the other party as “very unfavorable.” By 2016 those numbers had shot up to 58 percent and 55 percent, respectively.

But “very unfavorable” is just the tip of the partisan iceberg. Fully 45 percent of Republicans, and 41 percent of Democrats, view the other party as “a threat to the nation's well-being.” Those numbers rose significantly between 2014 and 2016.

This level of hostility is stunning. You can see how a certain type of person could get from a belief that the other party is a threat to the country, to a belief that it's up to them to do something about it — even something extreme. This viewpoint was explicitly articulated by Hodgkinson in a Facebook post in which he wrote, “Trump is a Traitor. Trump Has Destroyed Our Democracy. It’s Time to Destroy Trump & Co.”

Several decades ago, the polling suggests that for most Americans, their political party was part of who they were but not necessarily a core part of their personal identity, as it is for many people today.

One line of questioning illustrates that shift starkly: In 1960, roughly 5 percent of Democrats and Republicans told pollsters that they would be upset if their child married someone from a different political party. By 2010, those proportions stood at nearly 50 percent for Republicans and more than 30 percent for Democrats.