Donald Trump’s post-conventions polling slump seems to be having an effect on the Republican Party’s U.S. Senate candidates. We thought this might happen: There’s been an increasingly strong relationship between how a state votes for president and how it votes for Senate over the past few election cycles. And, indeed, Trump’s tumble has coincided with worsening GOP numbers in key states. It may cost the party the Senate.

Democrats need to gain a net of four or five seats to win control of the Senate, depending on whether Hillary Clinton or Trump wins the presidency. Before the conventions, polling in the 10 states whose Senate seats were most likely to flip between parties this November showed a pretty close race. Democratic candidates led in Illinois and Wisconsin, both of which would be pickups for their party. The Republican candidate was leading in Nevada (a seat that Democrats currently control). I didn’t include Indiana in my pre-convention analysis because of Democrat Evan Bayh’s late entrance into the race — we had just one partisan poll that included Bayh — but Democratic chances seemed good there (it would be another Democratic pickup). And Republicans led in the other competitive Senate races, all seats the GOP currently holds, so Democrats looked like they could pick up a net of two seats if everything stayed as it was and the polling leader in each state went on to win.

Since the conventions, however, Trump’s polling has worsened — overall and in states with key Senate races. In the eight states with competitive Senate races and both pre- and post-conventions polling, Trump had previously been down an average of about 6 percentage points; he’s now down an average of 9 points. And while Republican Senate candidates had been up by an average of a little more than 1 percentage point before the conventions in these eight states, they are now down by a little more than 1 point. That is, Republican Senate candidates in key states are still running ahead of Trump, but that cushion may no longer be enough to win now that Trump’s fortunes have worsened.

Six of the eight Republican candidates for Senate are polling worse than they were before the conventions.