If these numbers hold, McConnell’s majority is in danger. Assuming Republicans can’t hold Sen. Cory Gardner’s seat in Colorado, where earlier polls showed him trailing former Gov. John Hickenlooper by double digits, Democrats’ path to the majority is clear. If Biden wins the presidency and Democratic Senate challengers win in the four states where they’re currently leading, they’ve won a working 50-50 majority. (That includes the likelihood that Democratic Sen. Doug Jones of Alabama loses his seat this fall.)

That’s not including races in Iowa, Georgia, Kansas, and (now) Montana where Republicans are favored but Democrats are running competitive campaigns. Indeed, Montana Gov. Steve Bullock’s last-minute decision to run against Sen. Steve Daines is a sign of the newfound bullishness of Democrats’ prospects with Biden at the top of the ticket. Bullock starts out as an underdog, but it will be a competitive race that will force Republicans to spend money in a solidly conservative state.

Republican candidates have tied themselves so closely to Trump that they’re all dependent on his fortunes. That’s a risky place to be right now. Last month, the economy was booming and a socialist was on track to lead the Democratic ticket. This month, the stock market is falling, coronavirus is spreading, and a mainstream Democrat is positioned to become the presidential nominee. Trump’s reelection chances have suddenly taken a turn for the worse, and he’s threatening to take down the GOP’s Senate majority with him.