Dave Brat's stunning victory over House majority leader Eric Cantor is being hailed as a huge win for the Tea Party and immigration hawks, but might Brat actually owe his victory to Democrats, who were eligible to vote in Tuesday's open primary? That's a question Republican strategist Patrick Ruffini raised late last night on Twitter, where he pointed out that Brat performed very well in districts where Obama did best in 2012:

Ruffini also noted that former Democratic congressman Ben Jones, who played "Cooter" the Dukes of Hazzard and lost to Cantor in a 2002 election, wrote an open letter encouraging Democrats to vote for Brat. A Huffington Post story titled, "Cooter Has A Plan To Unseat Eric Cantor. It's So Crazy It Just Might Work," was "liked" on Facebook by 12,000 people. One Democrat recounts his decision to vote for Brat at Daily Kos.

But David Wasserman of the Cook Political Report dismissed the notion that Democrats swung the election to Brat: "This is a loss that can't be blamed on Democrats "crossing over" to vote in Virginia's open primary: Brat received his largest margins in VA-07's most conservative territory, including Hanover County (68 percent) and New Kent County (62 percent)."

Wasserman told me on Wednesday that he thinks there are only "a tiny handful of voters who would think to vote strategically" against Cantor. "I haven't ever seen a crossover vote that has meaningfully swayed the outcome of the race," he said.

Then again, we've never seen an upset as surprising as Brat's in recent memory. We can't know for sure how many Democrats voted in Tuesday's Republican primary, and it's possible that Democratic votes padded Brat's totals in the most conservative districts. What we do know is that Cantor's loss can much more clearly be attributed to the number of Republicans who abandoned him between 2012 and 2014.

In his 2012 primary, Cantor won more than 37,000 votes out of roughly 45,000 total votes cast. In 2014, Cantor won fewer than 29,000 votes out of the roughly 65,000 votes cast. So even as turnout increased nearly 50 percent between the two primary elections, Cantor's total number of votes dropped by 8,000. In other words, Cantor would have beaten Brat on Tuesday by a thousand votes if everyone who voted for him in 2012 voted for him again in 2014.

What happened between 2012 and 2014 that caused 8,000 people to change their votes from Cantor to Brat (or stay home)? The obvious answer is the backlash to immigration legislation that opponents dubbed amnesty.

As a member of leadership, Cantor "had to own flirtation with immigration reform," Wasserman told me. "I think the impact of [talk radio hosts] Mark Levin and Laura Ingraham was huge because they were able to bring activists together for rallies for Brat, and at each of those rallies, the Brat movement metastasized. Friends told friends. Neighbors told neighbors."

And that was enough for Brat to win the GOP nomination and shock the political world.

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