Harry Enten notices that of the states that elected Senators last week, 100% of them picked senators of the same party as the winner of their electoral votes -- that is, Trump states elected Republican senators, and Clinton states elected Democrat senators.
In the run-up to Election Day, we wondered whether more voters than normal would split their tickets because of Donald Trump's unique candidacy, perhaps voting for Republicans down-ballot but for Hillary Clinton in the presidential contest. Republican Senate candidates, unsure of how to deal with Trump, tried different approaches -- endorsing him, disavowing him, refusing to say whom they'd vote for. In the end, it didn't matter. Every state that elected a Republican candidate for Senate voted for Trump, and every state that elected a Democratic Senate candidate voted for Clinton.
The 2016 Senate elections were the most nationalized ever.
The amount of straight-ticket voting was unusual even for the highly polarized era we live in. Four years ago, for example, Democratic Senate candidates won in some states where President Obama lost by healthy margins, including Indiana, Missouri and North Dakota. Republicans, meanwhile, held their seat in Nevada even though Mitt Romney lost there by 7 percentage points.
The evidence provided doesn't support the claim. It's entirely possible that ticket-splitting increased, decreased, or stayed the same. If Adam votes for Trump and a Democrat senate candidate, and Betty votes for Clinton and a Republican senate candidate, then they both split their votes. The data provided tells you nothing about the prevalence of vote splitting.