FiveThirtyEight: “The 2018 election has become a tale of divided government: the House broke for Democrats, but the Senate held for Republicans — and what’s more, Republicans were even able to expand their majority in the Senate. The election has also become a tale of blue waves. But don’t those tales contradict one another? Not really. What the ‘split decision’ narrative sometimes misses is just how well Democrats performed in the Senate despite having to defend more seats than Republicans — and in territory that was largely more favorable to the GOP.”
“Much of this is overshadowed because Democrats did lose Senate seats… But if we look at a state’s partisan lean and the vote share margin in each Senate race, we see Democrats managed to outperform how their states leaned politically in almost every single race — including in the 10 states with a Democratic incumbent that President Trump won in 2016.”
However, First Read notes that Democratic performance in red states might have been their ceiling.