At CNN, Ron Brownstein points to the increasingly important role of presidential approval/disapproval in deciding downballot elections:
From the 1970s through the 1990s, House candidates still won competitive shares (around 25% to 40%) of voters who approved of a president from the other party. But that number plummeted after 2000: Under George W. Bush and Obama, only 12 to 15% of voters who approved of the president supported House candidates of the other party.
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As with many things, Trump intensified these trends. Widespread disapproval of his performance during his first two years powered the blue wave that swept Democrats to control of the House in 2018: 90% of voters who disapproved of Trump supported Democratic House candidates that year, the exit polls found.
Though Senate candidates have much more of an independent identity for voters than House members, the relationship was just as powerful in races for the upper chamber under Trump. Across the 2018 and 2020 elections combined, every Republican Senate candidate lost at least 89% of voters who disapproved of Trump, with only one exception — Susan Collins of Maine was the only Republican Senate candidate to hold their Democratic opponent to less than 89% support among voters who disapproved of Trump, or to carry more than 8% of those disapprovers, according to the exit polls in states and races where such polls were conducted. (Collins won fully 23% of voters who said they disapproved of Trump, en route to her surprisingly easy 2020 reelection on the same day he lost her state decisively.)
Even in governors’ races — which were long thought to be more insulated from national currents than Congressional contests — Gov. Scott Walker in Wisconsin, in his 2018 defeat, was the only GOP candidate during Trump’s term who carried even 10% of voters who disapproved of the president, according to exit polls.
Trump is uniquely polarizing.
Whatever the causes, the results of this month’s elections suggested that Trump’s impact on other contests remains uniquely intense. Significant majorities of voters in each of the major contests said they disapproved of his performance as president and overwhelming majorities of those disapprovers backed the Democrats: 93% of voters who disapproved of Trump voted for Mikie Sherrill in New Jersey, and 92% of them supported Democrat Abigail Spanberger in Virginia, according to the Voter Poll conducted by SRSS for a consortium of media organizations including CNN.
Maybe most telling, 89% of voters — there’s that number again — who disapproved of Trump supported Jay Jones, the Democratic Attorney General candidate in Virginia who had been battered by a scandal over text messages in which he had mused about shooting political rivals. The Republican candidates drew a comparable level of support among the much smaller share of voters who approved of Trump.