There is much speculation about whether Donald Trump’s nomination and presidential campaign could hurt down-ballot Republican candidates — particularly those in the U.S. Senate, where the GOP’s majority is already somewhat precarious. Trump is deeply unpopular with the electorate and this is making Senate Republicans nervous.
But three months of predictions from the forecasters at Good Judgment don’t suggest any clear impact of Trump’s likely nomination on the Republicans’ chances of retaining their Senate majority. Here is a graph that dates back to the middle of March:
During this time, Trump vanquished his remaining competitors and emerged as the presumptive GOP presidential nominee. Both the forecasters at Good Judgment, as well as the election betting markets, updated their estimated chance that he’d win the nomination.
But their forecasts for the Senate haven’t really changed, as you can see in the graph. The same thing is true at the betting markets. Both give the Democrats better-than-even odds of regaining a Senate majority, but neither seems to think that those chances have improved — even as Trump has become the likely nominee.
To be sure, there is some research suggesting that presidential candidates do have “coattails” in Senate races. The better a party’s presidential candidate does, the better that party’s Senate candidates do. We may therefore see the Democrats’ chances in the Senate increase if Trump’s chances in November decrease. But it hasn’t happened yet.