Trump's strength, though, meant that this didn't happen. At one point, it looked like Republicans might need to rely on crossover voting, people who would skip the presidential race or vote for Clinton but then vote for the Republican Senate candidate. In the end, that didn't happen either. Trump still received a lower percentage of the vote than most Republican senators, but his victories in these states — he won all but four — meant that Republican Senate candidates could rely on support from their base.
In Ohio, there was an opposite effect: A Clinton-Rob Portman vote. This is perhaps less surprising, given that Ohio's Republican establishment — led by Gov. John Kasich — was constantly struggling against Trump's political position.
In the end, this was the sort of crossover vote that Republicans thought they'd need. Portman didn't.
The four Republican Senate candidates who are losing as I write are also the four in states where Trump is also losing. Only in Nevada did Trump outperform the Senate candidate. That's the link that Republicans didn't always expect to see and are happy to take: voters, heavily Republican voters, voting for the Republican candidates.